Manhattan Project | Definition, Scientists, Timeline, Locations, Facts, & Significance

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class="md-content"> <div class="md-article-container template-desktop"> <div class="infinite-scroll-container article last"> <article class="article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded" data-topic-id="362098"> <div class="grid gx-0"> <div class="col-auto"> <div class="topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/event/Manhattan-Project">Manhattan Project</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/event/Manhattan-Project">Introduction & Top Questions</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref358250"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/event/Manhattan-Project#ref358250">Creation of the U.S. atomic weapons program</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref358251"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/event/Manhattan-Project#ref358251">Manhattan Project expansion under Groves and Oppenheimer</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref358252"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/event/Manhattan-Project#ref358252">The first atomic bombs: Trinity, Hiroshima, and Nagasaki</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref358253"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/event/Manhattan-Project#ref358253">Operation Crossroads and the end of the Manhattan Project</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/event/Manhattan-Project/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/Manhattan-Project">Quick Facts & Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10" href="https://www.britannica.com/event/Manhattan-Project/images-videos">Images, Videos & Interactives</a> <div class="slider js-slider position-relative d-inline-flex align-items-center mw-100 "> <div class="slider-container js-slider-container overflow-hidden d-flex overflow-hidden text-nowrap ml-15"> <a href="https://cdn.britannica.com/51/81351-050-37D356BA/atomic-bomb-test-Alamogordo-NM-July-16-1945.jpg" data-href="/media/1/362098/74664" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/51/81351-004-B24C7C08/atomic-bomb-test-Alamogordo-NM-July-16-1945.jpg" alt="Atomic bomb" height="50" /> </a> <a href="/video/J-Robert-Oppenheimer-atomic-bomb/284083" data-href="/media/1/362098/284083" class="media-overlay-link d-inline-block mr-5"> <div class="position-relative --aspect-ratio: 16/9"> <img 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They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <span class="text-gray-700"> Last Updated: <time datetime="2024-11-25T00:00:00CST" >Nov 25, 2024</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/event/Manhattan-Project/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn border-2 ai-ask-button btn border-2 module-spacing btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400 p-10 ml-5"> Ask the Chatbot a Question </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="qf-title font-weight-bold font-14 mb-10 text-center"> Quick Facts</div> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Date: </dt> <dd>1942 - 1945 </dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Key People: </dt> <dd><a href="/biography/Hans-Bethe">Hans Bethe</a></dd> <dd><a href="/biography/Enrico-Fermi">Enrico Fermi</a></dd> <dd><a href="/biography/Richard-Feynman">Richard Feynman</a></dd> <dd><a href="/biography/Edward-Teller">Edward Teller</a></dd> <dd><a href="/biography/Harold-Urey">Harold C. Urey</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>On the Web: </dt> <dd><a href="https://www.nationalww2museum.org/about-us/notes-museum/pope-physics-enrico-fermi-and-manhattan-project" target="_blank">The National WWII Museum - The Pope of Physics: Enrico Fermi and the Manhattan Project</a> (Nov. 12, 2024)</dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/Manhattan-Project"> See all related content </a> </div> </div> </div> </div><script type="application/ld+json"> { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type" : "Question", "name" : "<div>What led to the Manhattan Project?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "In 1939, American scientists, many of whom had fled from <a href=\"https:\/\/www.britannica.com\/topic\/fascism\">fascist<\/a> regimes in Europe, were aware of advances in <a href=\"https:\/\/www.britannica.com\/science\/nuclear-fission\">nuclear fission<\/a> and were concerned that <a href=\"https:\/\/www.britannica.com\/event\/Nazism\">Nazi Germany<\/a> might develop a nuclear weapon. The physicists <a href=\"https:\/\/www.britannica.com\/biography\/Leo-Szilard\">Leo Szilard<\/a> and <a href=\"https:\/\/www.britannica.com\/biography\/Eugene-Wigner\">Eugene Wigner<\/a> persuaded <a href=\"https:\/\/www.britannica.com\/biography\/Albert-Einstein\">Albert Einstein<\/a> to send a letter to U.S. President <a href=\"https:\/\/www.britannica.com\/biography\/Franklin-D-Roosevelt\">Franklin D. Roosevelt<\/a> warning him of that danger and advising him to establish an American nuclear research program. The Advisory Committee on Uranium was set up in response. The beginning of the Manhattan Project can be dated to December 6, 1941, with the creation of the Office of Scientific Research and Development, headed by <a href=\"https:\/\/www.britannica.com\/biography\/Vannevar-Bush\">Vannevar Bush<\/a>." } } , { "@type" : "Question", "name" : "<div>Who were the most important scientists associated with the Manhattan Project?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "American physicist <a href=\"https:\/\/www.britannica.com\/biography\/J-Robert-Oppenheimer\">J. Robert Oppenheimer<\/a> headed the Manhattan Project, with the goal of developing the <a href=\"https:\/\/www.britannica.com\/technology\/atomic-bomb\">atomic bomb<\/a>, and <a href=\"https:\/\/www.britannica.com\/biography\/Edward-Teller\">Edward Teller<\/a> was among the first recruited for the project. <a href=\"https:\/\/www.britannica.com\/biography\/Leo-Szilard\">Leo Szilard<\/a> and <a href=\"https:\/\/www.britannica.com\/biography\/Enrico-Fermi\">Enrico Fermi<\/a> built the first <a href=\"https:\/\/www.britannica.com\/technology\/nuclear-reactor\">nuclear reactor<\/a>. <a href=\"https:\/\/www.britannica.com\/biography\/Ernest-Lawrence\">Ernest Orlando Lawrence<\/a> was program chief in charge of the development of the electromagnetic process of separating <a href=\"https:\/\/www.britannica.com\/science\/uranium-235\">uranium-235<\/a>. <\/p><p>Other notable researchers included <a href=\"https:\/\/www.britannica.com\/biography\/Otto-Robert-Frisch\">Otto Frisch<\/a>, <a href=\"https:\/\/www.britannica.com\/biography\/Niels-Bohr\">Niels Bohr<\/a>, <a href=\"https:\/\/www.britannica.com\/biography\/Felix-Bloch\">Felix Bloch<\/a>, <a href=\"https:\/\/www.britannica.com\/biography\/James-Franck\">James Franck<\/a>, <a href=\"https:\/\/www.britannica.com\/biography\/Emilio-Segre\">Emilio Segr\u00E8<\/a>, <a href=\"https:\/\/www.britannica.com\/biography\/Klaus-Fuchs\">Klaus Fuchs<\/a>, <a href=\"https:\/\/www.britannica.com\/biography\/Hans-Bethe\">Hans Bethe<\/a>, and <a href=\"https:\/\/www.britannica.com\/biography\/John-von-Neumann\">John von Neumann<\/a>. The person who oversaw the Manhattan Project, however, was not a scientist. He was <a href=\"https:\/\/www.britannica.com\/biography\/Leslie-Richard-Groves\">Leslie Groves<\/a>, a brigadier general in the U.S. Army." } } , { "@type" : "Question", "name" : "<div>What did the Manhattan Project do?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The Manhattan Project produced the first <a href=\"https:\/\/www.britannica.com\/technology\/atomic-bomb\">atomic bomb<\/a>. Several lines of research <a href=\"https:\/\/www.britannica.com\/story\/timeline-of-the-manhattan-project\">were pursued simultaneously<\/a>. Both electromagnetic and fusion methods of separating the fissionable <a href=\"https:\/\/www.britannica.com\/science\/uranium-235\">uranium-235<\/a> from uranium-238 were explored at <a href=\"https:\/\/www.britannica.com\/place\/Oak-Ridge-Tennessee\">Oak Ridge<\/a> in Tennessee. 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The first test, on July 16, 1945, at <a href=\"https:\/\/www.britannica.com\/place\/Alamogordo\">Alamogordo<\/a> air force base in New Mexico, produced a massive nuclear explosion." } } , { "@type" : "Question", "name" : "<div>What were the immediate and long-term results of the Manhattan Project?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "Although many physicists were opposed to the actual use of the <a href=\"https:\/\/www.britannica.com\/technology\/atomic-bomb\">atomic bomb<\/a> created by the Manhattan Project, U.S. President <a href=\"https:\/\/www.britannica.com\/biography\/Harry-S-Truman\">Harry S. Truman<\/a> believed that the bomb would persuade <a href=\"https:\/\/www.britannica.com\/place\/Japan\">Japan<\/a> to surrender without requiring an American invasion. Accordingly, on August 6, 1945, a U.S. airplane dropped an atomic bomb on <a href=\"https:\/\/www.britannica.com\/place\/Hiroshima-Japan\">Hiroshima<\/a>, killing at least 70,000 people instantly (tens of thousands more died later of radiation poisoning). Three days later, another U.S. aircraft dropped a bomb on <a href=\"https:\/\/www.britannica.com\/place\/Nagasaki-Japan\">Nagasaki<\/a>. Since then, a number of countries have concluded that possession of <a href=\"https:\/\/www.britannica.com\/technology\/nuclear-weapon\">nuclear arms<\/a> is the best way to guarantee their safety, despite fears that <a href=\"https:\/\/www.britannica.com\/topic\/nuclear-proliferation\">nuclear proliferation<\/a> increases the chances of the use of such a weapon." } } ] } </script> <div class="top-questions qa-accordion d-flex flex-column module-spacing"><div class="font-weight-bold font-14 mb-5"> Top Questions </div><div id="intent-accordion" class="md-intent-accordion"><div class="top-question bg-gray-50 rounded" data-value="1"> <h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What led to the Manhattan Project?</div><em class="material-icons" data-icon="expand_more"></em></div></h3> <div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>In 1939, American scientists, many of whom had fled from <a href="https://www.britannica.com/topic/fascism" class="md-crosslink " data-show-preview="true">fascist</a> regimes in Europe, were aware of advances in <a href="https://www.britannica.com/science/nuclear-fission" class="md-crosslink " data-show-preview="true">nuclear fission</a> and were concerned that <a href="https://www.britannica.com/event/Nazism" class="md-crosslink " data-show-preview="true">Nazi Germany</a> might develop a nuclear weapon. The physicists <a href="https://www.britannica.com/biography/Leo-Szilard" class="md-crosslink " data-show-preview="true">Leo Szilard</a> and <a href="https://www.britannica.com/biography/Eugene-Wigner" class="md-crosslink " data-show-preview="true">Eugene Wigner</a> persuaded <a href="https://www.britannica.com/biography/Albert-Einstein" class="md-crosslink " data-show-preview="true">Albert Einstein</a> to send a letter to U.S. President <a href="https://www.britannica.com/biography/Franklin-D-Roosevelt" class="md-crosslink " data-show-preview="true">Franklin D. Roosevelt</a> warning him of that danger and advising him to establish an American nuclear research program. The Advisory Committee on Uranium was set up in response. The beginning of the Manhattan Project can be dated to December 6, 1941, with the creation of the Office of Scientific Research and Development, headed by <a href="https://www.britannica.com/biography/Vannevar-Bush" class="md-crosslink " data-show-preview="true">Vannevar Bush</a>.</p></div></div> </div><div class="top-question bg-gray-50 rounded" data-value="2"> <h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>Who were the most important scientists associated with the Manhattan Project?</div><em class="material-icons" data-icon="expand_more"></em></div></h3> <div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>American physicist <a href="https://www.britannica.com/biography/J-Robert-Oppenheimer" class="md-crosslink " data-show-preview="true">J. Robert Oppenheimer</a> headed the Manhattan Project, with the goal of developing the <a href="https://www.britannica.com/technology/atomic-bomb" class="md-crosslink " data-show-preview="true">atomic bomb</a>, and <a href="https://www.britannica.com/biography/Edward-Teller" class="md-crosslink " data-show-preview="true">Edward Teller</a> was among the first recruited for the project. <a href="https://www.britannica.com/biography/Leo-Szilard" class="md-crosslink " data-show-preview="true">Leo Szilard</a> and <a href="https://www.britannica.com/biography/Enrico-Fermi" class="md-crosslink " data-show-preview="true">Enrico Fermi</a> built the first <a href="https://www.britannica.com/technology/nuclear-reactor" class="md-crosslink " data-show-preview="true">nuclear reactor</a>. <a href="https://www.britannica.com/biography/Ernest-Lawrence" class="md-crosslink " data-show-preview="true">Ernest Orlando Lawrence</a> was program chief in charge of the development of the electromagnetic process of separating <a href="https://www.britannica.com/science/uranium-235" class="md-crosslink " data-show-preview="true">uranium-235</a>. </p><p>Other notable researchers included <a href="https://www.britannica.com/biography/Otto-Robert-Frisch" class="md-crosslink " data-show-preview="true">Otto Frisch</a>, <a href="https://www.britannica.com/biography/Niels-Bohr" class="md-crosslink " data-show-preview="true">Niels Bohr</a>, <a href="https://www.britannica.com/biography/Felix-Bloch" class="md-crosslink " data-show-preview="true">Felix Bloch</a>, <a href="https://www.britannica.com/biography/James-Franck" class="md-crosslink " data-show-preview="true">James Franck</a>, <a href="https://www.britannica.com/biography/Emilio-Segre" class="md-crosslink " data-show-preview="true">Emilio Segrè</a>, <a href="https://www.britannica.com/biography/Klaus-Fuchs" class="md-crosslink " data-show-preview="true">Klaus Fuchs</a>, <a href="https://www.britannica.com/biography/Hans-Bethe" class="md-crosslink " data-show-preview="true">Hans Bethe</a>, and <a href="https://www.britannica.com/biography/John-von-Neumann" class="md-crosslink " data-show-preview="true">John von Neumann</a>. The person who oversaw the Manhattan Project, however, was not a scientist. He was <a href="https://www.britannica.com/biography/Leslie-Richard-Groves" class="md-crosslink " data-show-preview="true">Leslie Groves</a>, a brigadier general in the U.S. Army.</p></div></div> </div><div class="top-question bg-gray-50 rounded" data-value="3"> <h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What did the Manhattan Project do?</div><em class="material-icons" data-icon="expand_more"></em></div></h3> <div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The Manhattan Project produced the first <a href="https://www.britannica.com/technology/atomic-bomb" class="md-crosslink " data-show-preview="true">atomic bomb</a>. Several lines of research <a href="https://www.britannica.com/story/timeline-of-the-manhattan-project" class="md-crosslink " data-show-preview="true">were pursued simultaneously</a>. Both electromagnetic and fusion methods of separating the fissionable <a href="https://www.britannica.com/science/uranium-235" class="md-crosslink " data-show-preview="true">uranium-235</a> from uranium-238 were explored at <a href="https://www.britannica.com/place/Oak-Ridge-Tennessee" class="md-crosslink " data-show-preview="true">Oak Ridge</a> in Tennessee. The production of plutonium-239, first achieved at the <a href="https://www.britannica.com/topic/University-of-Chicago" class="md-crosslink " data-show-preview="true">University of Chicago</a>, was further pursued at the <a href="https://www.britannica.com/topic/Hanford-Engineer-Works" class="md-crosslink " data-show-preview="true">Hanford Engineer Works</a> in Washington state. In the meantime, at <a href="https://www.britannica.com/place/Los-Alamos-New-Mexico" class="md-crosslink " data-show-preview="true">Los Alamos</a>, New Mexico, scientists found a way to bring the <a href="https://www.britannica.com/technology/fissile-material" class="md-crosslink " data-show-preview="true">fissionable material</a> to supercritical mass (and thus explosion) and to control the timing and devised a weapon to house it. The first test, on July 16, 1945, at <a href="https://www.britannica.com/place/Alamogordo" class="md-crosslink " data-show-preview="true">Alamogordo</a> air force base in New Mexico, produced a massive nuclear explosion.</p></div></div> </div><div class="top-question bg-gray-50 rounded" data-value="4"> <h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What were the immediate and long-term results of the Manhattan Project?</div><em class="material-icons" data-icon="expand_more"></em></div></h3> <div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>Although many physicists were opposed to the actual use of the <a href="https://www.britannica.com/technology/atomic-bomb" class="md-crosslink " data-show-preview="true">atomic bomb</a> created by the Manhattan Project, U.S. President <a href="https://www.britannica.com/biography/Harry-S-Truman" class="md-crosslink " data-show-preview="true">Harry S. Truman</a> believed that the bomb would persuade <a href="https://www.britannica.com/place/Japan" class="md-crosslink " data-show-preview="true">Japan</a> to surrender without requiring an American invasion. Accordingly, on August 6, 1945, a U.S. airplane dropped an atomic bomb on <a href="https://www.britannica.com/place/Hiroshima-Japan" class="md-crosslink " data-show-preview="true">Hiroshima</a>, killing at least 70,000 people instantly (tens of thousands more died later of radiation poisoning). Three days later, another U.S. aircraft dropped a bomb on <a href="https://www.britannica.com/place/Nagasaki-Japan" class="md-crosslink " data-show-preview="true">Nagasaki</a>. Since then, a number of countries have concluded that possession of <a href="https://www.britannica.com/technology/nuclear-weapon" class="md-crosslink " data-show-preview="true">nuclear arms</a> is the best way to guarantee their safety, despite fears that <a href="https://www.britannica.com/topic/nuclear-proliferation" class="md-crosslink " data-show-preview="true">nuclear proliferation</a> increases the chances of the use of such a weapon.</p></div><div class="connections border-top mt-15"><a href="/event/atomic-bombings-of-Hiroshima-and-Nagasaki" class="d-flex mt-15">atomic bombings of Hiroshima and Nagasaki</a>Learn more about the bombing raids that ended World War II.</div></div> </div><button class="show-more-button js-toggle-top-questions btn btn-unstyled font-14 d-flex pr-10 rounded-sm"><em class="material-icons" data-icon="expand_more"></em></button></div></div><div class="bg-gray-50 p-15 rounded module-spacing recent-news d-flex flex-column float-false"> <div> <h2 class="font-weight-bold font-14 m-0 d-inline"> News <span class="text-gray-600">•</span> </h2> <div class="recent-news-item first-recent-news-item d-inline"> <a class="font-14 gtm-ap-news-link" href="https://techcrunch.com/2024/11/20/this-week-in-ai-congressional-commission-warns-of-chinese-agi/" rel="nofollow">This Week in AI: Congressional commission warns of Chinese AGI</a> <span class="font-14 text-gray-600"> <span>•</span> Nov. 21, 2024, 2:18 AM ET (TechCrunch) <button class="btn btn-link d-inline p-0 font-12 js-toggle-recent-news"> <span class="text-gray-500">...</span><span>(Show more)</span> </button> </span> </div> </div> <div class="rest-of-recent-news-items"> <div class="recent-news-item mt-5"> <a class="font-14 gtm-ap-news-link" href="https://indianexpress.com/article/technology/artificial-intelligence/us-government-commission-pushes-manhattan-project-style-ai-initiative-9678896/" rel="nofollow">US government commission pushes Manhattan Project-style AI initiative</a> <span class="font-14 text-gray-600"> <span>•</span> Nov. 20, 2024, 1:50 AM ET (The Indian Express) </span> </div> <button class="js-toggle-recent-news d-flex btn btn-unstyled font-14 pr-10 rounded-sm mt-10" aria-label="Toggle additional news items"> Show less <em class="material-icons" data-icon="expand_less"></em> </button> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref9921"></span>Manhattan Project</strong>, U.S. government research project (1942–45) that produced the first <span id="ref9922"></span><a href="https://www.britannica.com/technology/atomic-bomb" class="md-crosslink " data-show-preview="true">atomic bombs</a>. <em>See</em> Britannica’s <a href="https://www.britannica.com/story/timeline-of-the-manhattan-project" class="md-crosslink " data-show-preview="true">interactive timeline</a> of the Manhattan Project.</p><span class="marker MOD1 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref358250"> <h2 class="h1">Creation of the U.S. atomic weapons program</h2> <span class="marker PREMOD2 mod-inline"></span><div class="assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100" data-type="other"><div class="slider-container js-slider-container overflow-hidden d-flex"><div class="rw-track d-flex align-items-center"><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="284083" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="245058"><a data-id="245058" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/J-Robert-Oppenheimer-atomic-bomb/-284083"><img src="https://cdn.britannica.com/58/245058-138-ADADBD4C/J-Robert-Oppenheimer-atomic-bomb.jpg?w=800&h=450&c=crop" alt="The true story of Oppenheimer and the atomic bomb" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/AVReymAy.m3u8" } ], "image": "https://cdn.britannica.com/58/245058-138-ADADBD4C/J-Robert-Oppenheimer-atomic-bomb.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/zSkfvKzC.vtt", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/4SGkhhnM.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">1 of 2</div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="245058">The true story of Oppenheimer and the atomic bomb</span><span>J. Robert Oppenheimer became involved in nuclear research in 1941. His biopic, <em>Oppenheimer</em>, was released in 2023.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/event/Manhattan-Project/images-videos">See all videos for this article</a></figcaption></figure></div><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="255917" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="223010"><a data-id="223010" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/did-you-know-Manhattan-Project/-255917"><img src="https://cdn.britannica.com/10/223010-138-D2A5B975/did-you-know-Manhattan-Project.jpg?w=800&h=450&c=crop" alt="What was the Manhattan Project?" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/yTDv29O2.m3u8" } ], "image": "https://cdn.britannica.com/10/223010-138-D2A5B975/did-you-know-Manhattan-Project.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/93SKrtCn", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/zT3lcg7U.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">2 of 2</div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="223010">What was the Manhattan Project?</span><span>Learn more about the Manhattan Project.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/event/Manhattan-Project/images-videos">See all videos for this article</a></figcaption></figure></div></div></div><button disabled="true" class="prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_left"></span></button><button disabled="true" class="next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_right"></span></button></div><p class="topic-paragraph">American scientists, many of them refugees from <a href="https://www.britannica.com/topic/fascism" class="md-crosslink " data-show-preview="true">fascist</a> <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="regimes" href="https://www.britannica.com/dictionary/regimes" data-type="EB">regimes</a> in Europe, took steps in 1939 to organize a project to exploit the newly recognized <a href="https://www.britannica.com/science/nuclear-fission" class="md-crosslink " data-show-preview="true">fission</a> process for military purposes. The first contact with the government was made by <span id="ref9923"></span>G.B. Pegram of <a href="https://www.britannica.com/topic/Columbia-University" class="md-crosslink " data-show-preview="true">Columbia University</a>, who arranged a conference between <span id="ref9924"></span><a href="https://www.britannica.com/biography/Enrico-Fermi" class="md-crosslink " data-show-preview="true">Enrico Fermi</a> and the Navy Department in March 1939. In the summer of 1939, <span id="ref9925"></span><a href="https://www.britannica.com/biography/Albert-Einstein" class="md-crosslink " data-show-preview="true">Albert Einstein</a> was persuaded by his fellow scientists to use his influence to present the military potential of an uncontrolled fission <a href="https://www.britannica.com/science/chain-reaction" class="md-crosslink autoxref " data-show-preview="true">chain reaction</a> to Pres. <span id="ref9926"></span><a href="https://www.britannica.com/biography/Franklin-D-Roosevelt" class="md-crosslink " data-show-preview="true">Franklin D. Roosevelt</a>. In February 1940, $6,000 was made available to start research under the supervision of a committee headed by L.J. Briggs, director of the National <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="Bureau" href="https://www.britannica.com/dictionary/Bureau" data-type="EB">Bureau</a> of Standards (later <a href="https://www.britannica.com/topic/National-Institute-of-Standards-and-Technology" class="md-crosslink " data-show-preview="true">National Institute of Standards and Technology</a>). On December 6, 1941, the project was put under the direction of the Office of Scientific Research and Development, headed by <span id="ref9927"></span><a href="https://www.britannica.com/biography/Vannevar-Bush" class="md-crosslink " data-show-preview="true">Vannevar Bush</a>.</p><span class="marker MOD2 mod-inline"></span> <span class="marker PREMOD3 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="181860" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/77/128377-004-D775CBDB/Leslie-Richard-Groves.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/181860"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/77/128377-004-D775CBDB/Leslie-Richard-Groves.jpg?w=300"><img src="https://cdn.britannica.com/77/128377-004-D775CBDB/Leslie-Richard-Groves.jpg?w=300" alt="Leslie Groves" data-width="349" data-height="450" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/77/128377-004-D775CBDB/Leslie-Richard-Groves.jpg" data-href="/media/1/362098/181860">Leslie Groves</a><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">After the U.S. entered <a href="https://www.britannica.com/event/World-War-II" class="md-crosslink " data-show-preview="true">World War II</a>, the War Department was given joint responsibility for the project, because by mid-1942 it was obvious that a vast array of pilot plants, laboratories, and manufacturing facilities would have to be constructed by the <a href="https://www.britannica.com/topic/US-Army-Corps-of-Engineers" class="md-crosslink " data-show-preview="true">U.S. Army Corps of Engineers</a> for the assembled scientists to carry out their mission. In June 1942 the <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="Corps" href="https://www.britannica.com/dictionary/Corps" data-type="EB">Corps</a> of Engineers’ Manhattan District was initially assigned management of the construction work (because much of the early research had been performed at Columbia University, in <a href="https://www.britannica.com/place/Manhattan-New-York-City" class="md-crosslink " data-show-preview="true">Manhattan</a>), and in September 1942 Brig. Gen. <span id="ref9928"></span><a href="https://www.britannica.com/biography/Leslie-Richard-Groves" class="md-crosslink " data-show-preview="true">Leslie R. Groves</a> was placed in charge of all Army activities (chiefly engineering activities) relating to the project. “Manhattan Project” became the code name for research work that would extend across the country.</p><a class="link-module shadow-sm d-block qa-read-more-module" href="/technology/nuclear-weapon/Founding-the-Manhattan-Project#ref521115" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/13/94113-050-043A9DE8/test-thermonuclear-weapon-Enewetak-atoll-Marshall-Islands-Nov-1-1952.jpg" alt="A test of a U.S. hydrogen bomb in the Marshall Islands" class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-navy-dark">More From Britannica</div> <div class="font-weight-semi-bold mt-5">nuclear weapon: Founding the Manhattan Project</div> </div> </a><span class="marker MOD3 mod-inline"></span> <div class="mb-20"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="284272" data-asm-type="infogram"><div class="md-assembly-wrapper card-media " data-type="infogram"><script id="infogram_0__/IsLVzAn8O2U5rHxV8SGM" src="https://e.infogram.com/js/dist/embed.js?Itp" type="text/javascript" title="Manhattan Project interactive timeline"></script></div></figure></div></div> </section> <span class="marker h3"></span><section data-level="1" id="ref358251"> <h2 class="h1">Manhattan Project expansion under Groves and Oppenheimer</h2> <span class="marker PREMOD5 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="255918" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/97/222597-050-DAACF5E2/infographic-Manhattan-Project-atomic-bombs.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/255918"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/97/222597-050-DAACF5E2/infographic-Manhattan-Project-atomic-bombs.jpg"><img src="https://cdn.britannica.com/97/222597-050-DAACF5E2/infographic-Manhattan-Project-atomic-bombs.jpg?w=300" alt="Timeline of the Manhattan Project" data-width="800" data-height="2000" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/97/222597-050-DAACF5E2/infographic-Manhattan-Project-atomic-bombs.jpg" data-href="/media/1/362098/255918">Timeline of the Manhattan Project</a><span>An infographic timeline of key dates in the Manhattan Project.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">It was known in 1940 that German scientists were working on a similar project and that the British were also exploring the problem. In the fall of 1941 Manhattan Project chemist <span id="ref9929"></span><a href="https://www.britannica.com/biography/Harold-Urey" class="md-crosslink " data-show-preview="true">Harold C. Urey</a> accompanied Pegram to England to attempt to set up a cooperative effort, and by 1943 a combined policy committee was established with Great Britain and <a href="https://www.britannica.com/place/Canada" class="md-crosslink autoxref " data-show-preview="true">Canada</a>. In that year a number of British and Canadian scientists moved to the <a href="https://www.britannica.com/place/United-States" class="md-crosslink autoxref " data-show-preview="true">United States</a> to join the project.</p><span class="marker MOD5 mod-inline"></span> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">If the project were to achieve <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="timely" href="https://www.britannica.com/dictionary/timely" data-type="EB">timely</a> success, several lines of <a href="https://www.britannica.com/topic/research-and-development" class="md-crosslink autoxref " data-show-preview="true">research and development</a> had to be carried on simultaneously before it was certain whether any might succeed. The explosive materials then had to be produced and be made suitable for use in an actual weapon.</p><span class="marker MOD6 mod-inline"></span> <span class="marker PREMOD7 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="111670" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/05/114405-050-B04AD3DB/fission-bomb-designs-arrangement-material.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/111670"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/05/114405-050-B04AD3DB/fission-bomb-designs-arrangement-material.jpg"><img src="https://cdn.britannica.com/05/114405-050-B04AD3DB/fission-bomb-designs-arrangement-material.jpg?w=300" alt="Fission bomb" data-width="913" data-height="1600" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/05/114405-050-B04AD3DB/fission-bomb-designs-arrangement-material.jpg" data-href="/media/1/362098/111670">Fission bomb</a><span>The three most common fission bomb designs, which vary considerably in material and arrangement.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph"><span id="ref9930"></span><a href="https://www.britannica.com/science/uranium-235" class="md-crosslink " data-show-preview="true">Uranium-235</a>, the essential fissionable component of the postulated bomb, cannot be separated from its natural companion, the much more abundant <span id="ref9931"></span><a href="https://www.britannica.com/science/uranium-238" class="md-crosslink ">uranium-238</a>, by chemical means; the atoms of these respective <a href="https://www.britannica.com/science/isotope" class="md-crosslink " data-show-preview="true">isotopes</a> must rather be separated from each other by physical means. Several physical methods to do this were intensively explored, and two were chosen—the electromagnetic process developed at the <a href="https://www.britannica.com/topic/University-of-California" class="md-crosslink " data-show-preview="true">University of California</a>, <a href="https://www.britannica.com/place/Berkeley-California" class="md-crosslink autoxref " data-show-preview="true">Berkeley</a>, under <span id="ref9932"></span><a href="https://www.britannica.com/biography/Ernest-Lawrence" class="md-crosslink " data-show-preview="true">Ernest Orlando Lawrence</a> and the <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="diffusion" href="https://www.merriam-webster.com/dictionary/diffusion" data-type="MW">diffusion</a> process developed under Urey at Columbia University. Both of these processes, particularly the diffusion method, required large, complex facilities and huge amounts of <a href="https://www.britannica.com/technology/electric-power" class="md-crosslink autoxref " data-show-preview="true">electric power</a> to produce even small amounts of separated uranium-235. <span id="ref9933"></span><a href="https://www.britannica.com/biography/Philip-Hauge-Abelson" class="md-crosslink " data-show-preview="true">Philip Hauge Abelson</a> developed a third method called thermal diffusion, which was also used for a time to effect a preliminary separation. These methods were put into production at a 70-square-mile (180-square-km) tract near <a href="https://www.britannica.com/place/Knoxville" class="md-crosslink " data-show-preview="true">Knoxville</a>, <a href="https://www.britannica.com/place/Tennessee" class="md-crosslink " data-show-preview="true">Tennessee</a>, originally known as the Clinton Engineer Works, later as <span id="ref9934"></span><a href="https://www.britannica.com/place/Oak-Ridge-Tennessee" class="md-crosslink " data-show-preview="true">Oak Ridge</a>.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Get Unlimited Access</div> <div class="h4 font-weight-semi-bold">Try Britannica Premium for free and discover more.</div> </div> <div class="student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto"> <a class="btn btn-m btn-orange" href="https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=black-friday-2024">Subscribe</a> </div> </div> </div> </DIV></div><span class="marker MOD7 mod-inline"></span> <span class="marker PREMOD8 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="177393" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/37/163337-050-71CBA247/Scientists-world-chain-reaction-Chicago-Pile-No-1957.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/177393"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/37/163337-050-71CBA247/Scientists-world-chain-reaction-Chicago-Pile-No-1957.jpg?w=300"><img src="https://cdn.britannica.com/37/163337-050-71CBA247/Scientists-world-chain-reaction-Chicago-Pile-No-1957.jpg?w=300" alt="First self-sustaining nuclear chain reaction" data-width="1600" data-height="845" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/37/163337-050-71CBA247/Scientists-world-chain-reaction-Chicago-Pile-No-1957.jpg" data-href="/media/1/362098/177393">First self-sustaining nuclear chain reaction</a><span>Scientists observing the world's first self-sustaining nuclear chain reaction, in the Chicago Pile No. 1, December 2, 1942. Photograph of an original painting by Gary Sheehan, 1957.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">Only one method was available for the production of the <a href="https://www.britannica.com/technology/fissile-material" class="md-crosslink autoxref " data-show-preview="true">fissionable material</a> <span id="ref9935"></span><a href="https://www.britannica.com/science/plutonium-239" class="md-crosslink ">plutonium-239</a>. It was developed at the metallurgical laboratory of the <span id="ref9936"></span><a href="https://www.britannica.com/topic/University-of-Chicago" class="md-crosslink " data-show-preview="true">University of Chicago</a> under the direction of <span id="ref9937"></span><a href="https://www.britannica.com/biography/Arthur-Holly-Compton" class="md-crosslink " data-show-preview="true">Arthur Holly Compton</a> and involved the <a href="https://www.britannica.com/science/transmutation" class="md-crosslink autoxref " data-show-preview="true">transmutation</a> in a reactor pile of uranium-238. In December 1942 Fermi finally succeeded in producing and controlling a fission chain reaction in this reactor pile at Chicago.</p><span class="marker MOD8 mod-inline"></span> <span class="marker PREMOD9 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="200582" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/37/183537-050-F43BFA6C/World-War-II-first-atomic-bombs-test-Los-Alamos-New-Mexico-detonation-Hiroshima-Nagasaki-Japan-1945.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/200582"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/37/183537-050-F43BFA6C/World-War-II-first-atomic-bombs-test-Los-Alamos-New-Mexico-detonation-Hiroshima-Nagasaki-Japan-1945.jpg"><img src="https://cdn.britannica.com/37/183537-050-F43BFA6C/World-War-II-first-atomic-bombs-test-Los-Alamos-New-Mexico-detonation-Hiroshima-Nagasaki-Japan-1945.jpg?w=300" alt="Discover more about the first atomic bombs" data-width="2000" data-height="1344" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/37/183537-050-F43BFA6C/World-War-II-first-atomic-bombs-test-Los-Alamos-New-Mexico-detonation-Hiroshima-Nagasaki-Japan-1945.jpg" data-href="/media/1/362098/200582">Discover more about the first atomic bombs</a><span>The first atomic bomb was detonated on July 16, 1945, in New Mexico as part of the U.S. government program called the Manhattan Project. The United States then used atomic bombs on Hiroshima and Nagasaki in Japan on August 6 and 9, respectively, killing about 210,000 people. This infographic describes these early bombs, how they worked, and how they were used.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">Quantity production of plutonium-239 required the construction of a reactor of great size and power that would release about 25,000 kilowatt-hours of heat for each gram of <a href="https://www.britannica.com/science/plutonium" class="md-crosslink autoxref " data-show-preview="true">plutonium</a> produced. This required the development of chemical extraction procedures that would work under conditions never before <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="encountered" href="https://www.britannica.com/dictionary/encountered" data-type="EB">encountered</a>. An intermediate step in putting this method into production was taken with the construction of a medium-size reactor at Oak Ridge. The large-scale production reactors were built on an isolated 1,000-square-mile (2,600-square-km) tract on the <a href="https://www.britannica.com/place/Columbia-River" class="md-crosslink " data-show-preview="true">Columbia River</a> north of <a href="https://www.britannica.com/place/Pasco-Washington" class="md-crosslink " data-show-preview="true">Pasco</a>, Washington—the <span id="ref9938"></span><a href="https://www.britannica.com/topic/Hanford-Engineer-Works" class="md-crosslink " data-show-preview="true">Hanford Engineer Works</a>.</p><span class="marker MOD9 mod-inline"></span> <span class="marker PREMOD10 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="254710" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/55/187755-050-25A513FF/J-Robert-Oppenheimer.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/254710"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/55/187755-050-25A513FF/J-Robert-Oppenheimer.jpg?w=300"><img src="https://cdn.britannica.com/55/187755-050-25A513FF/J-Robert-Oppenheimer.jpg?w=300" alt="J. Robert Oppenheimer" data-width="1258" data-height="1600" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/55/187755-050-25A513FF/J-Robert-Oppenheimer.jpg" data-href="/media/1/362098/254710">J. Robert Oppenheimer</a><span>Scientist J. Robert Oppenheimer, c. 1944.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">Before 1943, work on the design and functioning of the bomb itself was largely theoretical, based on fundamental experiments carried out at a number of different locations. In that year a laboratory directed by <span id="ref9939"></span><a href="https://www.britannica.com/biography/J-Robert-Oppenheimer" class="md-crosslink " data-show-preview="true">J. Robert Oppenheimer</a> was created on an isolated mesa at <span id="ref9940"></span><a href="https://www.britannica.com/place/Los-Alamos-New-Mexico" class="md-crosslink " data-show-preview="true">Los Alamos</a>, <a href="https://www.britannica.com/place/New-Mexico" class="md-crosslink " data-show-preview="true">New Mexico</a>, 34 miles (55 km) north of <a href="https://www.britannica.com/place/Santa-Fe-New-Mexico" class="md-crosslink " data-show-preview="true">Santa Fe</a>. This laboratory was tasked with developing methods to reduce the fissionable products of the production plants to pure metal and fabricate the metal to required shapes. Methods of rapidly bringing together amounts of fissionable material to achieve a supercritical mass (and thus a nuclear explosion) had to be <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="devised" href="https://www.britannica.com/dictionary/devised" data-type="EB">devised</a>, along with the actual construction of a deliverable weapon that would be dropped from a plane and fused to detonate at the proper moment in the air above the target. Most of these problems had to be solved before any appreciable amount of fissionable material could be produced, so that the first adequate amounts could be used at the fighting front with minimum delay.</p><span class="marker MOD10 mod-inline"></span> <span class="marker PREMOD11 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="243876" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/72/200272-050-88E0D037/J-Robert-Oppenheimer-General-Leslie-Groves-Trinity-test-site-Alamogordo-New-Mexico-September-1945.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/243876"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/72/200272-050-88E0D037/J-Robert-Oppenheimer-General-Leslie-Groves-Trinity-test-site-Alamogordo-New-Mexico-September-1945.jpg?w=300"><img src="https://cdn.britannica.com/72/200272-050-88E0D037/J-Robert-Oppenheimer-General-Leslie-Groves-Trinity-test-site-Alamogordo-New-Mexico-September-1945.jpg?w=300" alt="J. Robert Oppenheimer and Leslie R. Groves" data-width="1276" data-height="1600" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/72/200272-050-88E0D037/J-Robert-Oppenheimer-General-Leslie-Groves-Trinity-test-site-Alamogordo-New-Mexico-September-1945.jpg" data-href="/media/1/362098/243876">J. Robert Oppenheimer and Leslie R. Groves</a><span>At the Trinity test site in Alamogordo, New Mexico, J. Robert Oppenheimer (left) and Gen. Leslie R. Groves examining the remains of a steel tower, September 1945.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">By the summer of 1945, amounts of plutonium-239 sufficient to produce a nuclear explosion had become available from the Hanford Works, and weapon development and design were sufficiently advanced so that an actual field test of a nuclear explosive could be scheduled. Such a test was no simple affair. Elaborate and complex equipment had to be assembled to provide a complete <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="diagnosis" href="https://www.merriam-webster.com/dictionary/diagnosis" data-type="MW">diagnosis</a> of success or failure. By this time the original $6,000 authorized for the Manhattan Project had grown to $2 billion.</p><span class="marker MOD11 mod-inline"></span> </section> <span class="marker h4"></span><section data-level="1" id="ref358252"> <h2 class="h1">The first atomic bombs: Trinity, Hiroshima, and Nagasaki</h2> <span class="marker PREMOD12 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="4333" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/32/6032-050-69181D3C/atomic-bomb-test-Alamogordo-New-Mexico-July-16-1945.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/4333"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/32/6032-050-69181D3C/atomic-bomb-test-Alamogordo-New-Mexico-July-16-1945.jpg?w=300"><img src="https://cdn.britannica.com/32/6032-050-69181D3C/atomic-bomb-test-Alamogordo-New-Mexico-July-16-1945.jpg?w=300" alt="Atomic bomb: first test" data-width="1600" data-height="1384" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/32/6032-050-69181D3C/atomic-bomb-test-Alamogordo-New-Mexico-July-16-1945.jpg" data-href="/media/1/362098/4333">Atomic bomb: first test</a><span>First atomic bomb test, near Alamogordo, New Mexico, July 16, 1945.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">The first atomic bomb was exploded at 5:30 <span class="text-smallcaps">am</span> on July 16, 1945, at the <a href="https://www.britannica.com/place/Alamogordo" class="md-crosslink " data-show-preview="true">Alamogordo</a> air base 120 miles (193 km) south of <a href="https://www.britannica.com/place/Albuquerque" class="md-crosslink " data-show-preview="true">Albuquerque</a>, New Mexico. Oppenheimer had called the site “Trinity” in reference to one of <a href="https://www.britannica.com/biography/John-Donne" class="md-crosslink " data-show-preview="true">John Donne</a>’s <a href="https://www.britannica.com/topic/Holy-Sonnets" class="md-crosslink " data-show-preview="true">Holy Sonnets</a>. The bomb—a plutonium implosion device called <em>Gadget</em>—was raised to the top of a 100-foot (30-meer) steel tower that was <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="designated" href="https://www.britannica.com/dictionary/designated" data-type="EB">designated</a> “Zero.” The area at the base of the tower was marked as “Ground Zero,” a term that would pass into common parlance to describe the center of an (often catastrophic) event. The tower was surrounded by scientific equipment, with remote monitoring taking place in bunkers occupied by scientists and a few dignitaries 10,000 yards (9 km) away. The explosion came as an intense light flash, a sudden wave of heat, and later a tremendous roar as the <a href="https://www.britannica.com/science/shock-wave" class="md-crosslink autoxref " data-show-preview="true">shock wave</a> passed and echoed in the valley. A ball of fire rose rapidly, followed by a mushroom cloud extending to 40,000 feet (12,200 meters). The bomb generated an explosive power equivalent to 15,000 to 20,000 tons of <a href="https://www.britannica.com/science/trinitrotoluene" class="md-crosslink " data-show-preview="true">trinitrotoluene </a>(TNT); the tower was completely vaporized and the surrounding desert surface fused to glass for a radius of 800 yards (730 meters).</p><span class="marker MOD12 mod-inline"></span> <span class="marker PREMOD13 mod-inline"></span><div class="assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100" data-type="other"><div class="slider-container js-slider-container overflow-hidden d-flex"><div class="rw-track d-flex align-items-center"><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="254714" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/32/194732-050-9D77FB77/Hiroshima-Japan-bomb-devastation-1945.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/254714"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/32/194732-050-9D77FB77/Hiroshima-Japan-bomb-devastation-1945.jpg?w=300"><img src="https://cdn.britannica.com/32/194732-050-9D77FB77/Hiroshima-Japan-bomb-devastation-1945.jpg?w=300" alt="Aftermath of the atomic bombing of Hiroshima" data-width="1424" data-height="1004" loading="eager"></picture><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">1 of 2</div><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/32/194732-050-9D77FB77/Hiroshima-Japan-bomb-devastation-1945.jpg" data-href="/media/1/362098/254714">Aftermath of the atomic bombing of Hiroshima</a><span>Ruins of Hiroshima after the detonation of a U.S. atomic bomb on August 6, 1945. The Hiroshima Prefectural Industrial Promotion Hall (now known as the Atomic Bomb Dome) is visible in the distance.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="18899" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="22983"><a data-id="22983" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/Japan-Hiroshima-B-29-Superfortress-Enola-Gay-dropping-August-6-1945/-18899"><img src="https://cdn.britannica.com/83/22983-138-ADD07B68/Japan-Hiroshima-B-29-Superfortress-Enola-Gay-dropping-August-6-1945.jpg?w=800&h=450&c=crop" alt="Watch U.S. B-29 Superfortress Enola Gay decimate Hiroshima with a nuclear bomb in the Pacific War" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/XMOCDFEh.m3u8" } ], "image": "https://cdn.britannica.com/83/22983-138-ADD07B68/Japan-Hiroshima-B-29-Superfortress-Enola-Gay-dropping-August-6-1945.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/7Z7JNxOl", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/VJO19GFg.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">2 of 2</div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="22983">Watch U.S. B-29 Superfortress <em>Enola Gay</em> decimate Hiroshima with a nuclear bomb in the Pacific War</span><span>The B-29 Superfortress <em>Enola Gay</em> took off from the Mariana Islands on August 6, 1945, bound for Hiroshima, Japan, where, by dropping an atomic bomb, it heralded a new and terrible concept of warfare. From <em>The Second World War: Allied Victory</em> (1963), a documentary by Encyclopædia Britannica Educational Corporation.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/event/Manhattan-Project/images-videos">See all videos for this article</a></figcaption></figure></div></div></div><button disabled="true" class="prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_left"></span></button><button disabled="true" class="next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_right"></span></button></div><p class="topic-paragraph">The following month, two other atomic bombs produced by the project, the first using uranium-235 and the second using plutonium, were dropped on the Japanese cities of Hiroshima and Nagasaki. Neither city had been attacked during the U.S. <a href="https://www.britannica.com/event/strategic-bombing-during-World-War-II" class="md-crosslink " data-show-preview="true">strategic bombing campaign</a> until that point, and planners wished to demonstrate the destructive power of the bombs. <a href="https://www.britannica.com/place/Hiroshima-Japan" class="md-crosslink " data-show-preview="true">Hiroshima</a> was selected as the primary target because of its military value; the city served as the headquarters of the Japanese Second Army. On August 6, 1945, at about 8:15 <span class="text-smallcaps">am</span> local time, a U.S. <a href="https://www.britannica.com/technology/B-29" class="md-crosslink " data-show-preview="true">B-29 bomber</a> released a gun assembly fission bomb—dubbed <em>Little Boy</em>—above Hiroshima. The weapon detonated at an <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="altitude" href="https://www.britannica.com/dictionary/altitude" data-type="EB">altitude</a> of 1,900 feet (580 meters), and the explosive yield was estimated to be the equivalent of 15,000 tons of TNT. Some 70,000 people were killed instantly, and by the end of the year the death toll had surpassed 100,000. Two-thirds of the city area was destroyed.</p><span class="marker MOD13 mod-inline"></span> <span class="marker PREMOD14 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="109345" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/42/112542-050-E5BBDB20/atomic-bomb-Hiroshima-Japan-port-Nagasaki-Aug-8-1945.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/109345"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/42/112542-050-E5BBDB20/atomic-bomb-Hiroshima-Japan-port-Nagasaki-Aug-8-1945.jpg?w=300"><img src="https://cdn.britannica.com/42/112542-050-E5BBDB20/atomic-bomb-Hiroshima-Japan-port-Nagasaki-Aug-8-1945.jpg?w=300" alt="Atomic bomb at Nagasaki, Japan" data-width="1265" data-height="1600" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/42/112542-050-E5BBDB20/atomic-bomb-Hiroshima-Japan-port-Nagasaki-Aug-8-1945.jpg" data-href="/media/1/362098/109345">Atomic bomb at Nagasaki, Japan</a><span>On August 9, 1945, three days after detonating a uranium-fueled atomic bomb over Hiroshima, Japan, the United States dropped a plutonium-fueled atomic bomb over the Japanese port of Nagasaki.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">By the morning of August 9, 1945, the <a href="https://www.britannica.com/place/Soviet-Union" class="md-crosslink " data-show-preview="true">Soviet Union</a> had declared war on Japan, but the Japanese government had not yet communicated its intent to surrender to the <a href="https://www.britannica.com/topic/Allied-powers-World-War-II" class="md-crosslink " data-show-preview="true">Allies</a>. A B-29 carrying <a href="https://www.britannica.com/topic/Fat-Man" class="md-crosslink " data-show-preview="true"><em>Fat Man</em></a>—a plutonium implosion bomb similar to the one used in the Trinity test—was initially dispatched to Kokura (now part of <a href="https://www.britannica.com/place/Kitakyushu" class="md-crosslink " data-show-preview="true">Kitakyūshū</a>, Japan). Thick clouds and <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="haze" href="https://www.britannica.com/dictionary/haze" data-type="EB">haze</a> over Kokura prevented the bombardier from sighting the designated aimpoint, however, and the bomber proceeded to its secondary target, the port city of <a href="https://www.britannica.com/place/Nagasaki-Japan" class="md-crosslink " data-show-preview="true">Nagasaki</a>. At 11:02 <span class="text-smallcaps">am</span> <em>Fat Man</em> exploded at an altitude of 1,650 feet (500 meters) northwest of the city center. The bomb detonated with the explosive force of 21,000 tons of TNT. An estimated 40,000 people were killed instantly, and at least 30,000 more would die from their injuries and radiation poisoning by the end of the year. About 40 percent of the city’s buildings were completely destroyed or severely damaged. Due to the area’s uneven terrain, a significant part of Nagasaki—particularly in the southeastern industrial and government district—was relatively <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="unscathed" href="https://www.britannica.com/dictionary/unscathed" data-type="EB">unscathed</a>. The Japanese initiated surrender negotiations the next day. By this point, Groves had notified U.S. Pres. <a href="https://www.britannica.com/biography/Harry-S-Truman" class="md-crosslink " data-show-preview="true">Harry S. Truman</a> that another bomb would be ready for delivery within a week.</p><span class="marker MOD14 mod-inline"></span> <span class="marker PREMOD15 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="109343" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/48/112548-050-16D0DEC0/woman-Photograph-skin-pattern-kimono-exposure-radiation.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/109343"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/48/112548-050-16D0DEC0/woman-Photograph-skin-pattern-kimono-exposure-radiation.jpg?w=300"><img src="https://cdn.britannica.com/48/112548-050-16D0DEC0/woman-Photograph-skin-pattern-kimono-exposure-radiation.jpg?w=300" alt="Ionizing radiation injury from atomic bomb" data-width="1468" data-height="1600" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/48/112548-050-16D0DEC0/woman-Photograph-skin-pattern-kimono-exposure-radiation.jpg" data-href="/media/1/362098/109343">Ionizing radiation injury from atomic bomb</a><span>Photograph of a woman's skin burned in the pattern of the kimono she was wearing at the time of her exposure to radiation from one of the atomic bombs dropped by the United States on Japan.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">On September 2, 1945, a Japanese delegation signed formal surrender documents on the deck of the USS <em>Missouri</em>. Shortly after the conclusion of hostilities, Manhattan Project physicist Philip Morrison traveled to Hiroshima at the request of the War Department to study the effects of the atomic bomb. Characterizing the bomb as “preeminently a weapon of saturation,” he said, “It destroys so quickly and so completely such a large area that defense is hopeless.” Horrified by what he had <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="witnessed" href="https://www.britannica.com/dictionary/witnessed" data-type="EB">witnessed</a>, Morrison would spend the rest of his life campaigning against nuclear weapons and a potential “third bomb.”</p><span class="marker MOD15 mod-inline"></span> </section> <span class="marker h5"></span><section data-level="1" id="ref358253"> <h2 class="h1">Operation Crossroads and the end of the Manhattan Project</h2> <span class="marker PREMOD16 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="283901" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/02/246202-050-04570921/Nuclear-test-Able-Operations-Crossroads-Bikini-Atoll-July-1-1941.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/283901"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/02/246202-050-04570921/Nuclear-test-Able-Operations-Crossroads-Bikini-Atoll-July-1-1941.jpg?w=300"><img src="https://cdn.britannica.com/02/246202-050-04570921/Nuclear-test-Able-Operations-Crossroads-Bikini-Atoll-July-1-1941.jpg?w=300" alt="Operation Crossroads" data-width="1600" data-height="818" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/02/246202-050-04570921/Nuclear-test-Able-Operations-Crossroads-Bikini-Atoll-July-1-1941.jpg" data-href="/media/1/362098/283901">Operation Crossroads</a><span>“Able,” the first peacetime atomic weapons test, conducted at Bikini atoll, July 1, 1946.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">After the war, the Manhattan Project oversaw Operation Crossroads, a military-scientific experiment conducted at <a href="https://www.britannica.com/place/Bikini-atoll-Marshall-Islands" class="md-crosslink " data-show-preview="true">Bikini</a> atoll in the South Pacific in 1946. “Able,” the first peacetime atomic weapons test, was carried out on July 1, 1946. In attendance were some 42,000 U.S. military personnel, as well as more than 100 journalists and representatives from a dozen foreign countries. A 20-kiloton atomic bomb was dropped from a B-29 and exploded at an altitude of about 520 feet (158 meters) over a fleet of about 80 decommissioned World War II naval vessels. Only five ships were sunk by the blast, and, although several more were damaged, the majority survived the explosion relatively unscathed. Within a day, radiation levels had subsided enough for the ships to be boarded and inspected. Press and foreign military observers seemed underwhelmed that the blast had not vaporized the assembled ships, but such an appraisal discounted the debilitating effect that radiation would have had on a ship’s crew. Many test animals placed throughout the fleet quickly <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="succumbed" href="https://www.merriam-webster.com/dictionary/succumbed" data-type="MW">succumbed</a> to <a href="https://www.britannica.com/science/ionizing-radiation-injury" class="md-crosslink autoxref " data-show-preview="true">radiation sickness</a>, confirming a prediction in the <em>Bulletin of the Atomic Scientists</em> that “a large ship, about a mile away from the explosion, would escape sinking, but the crew would be killed by the deadly burst of radiations from the bomb, and only a ghost ship would remain, floating unattended on the vast waters of the ocean.”</p><span class="marker MOD16 mod-inline"></span> <span class="marker PREMOD17 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="283506" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/60/231260-050-F8D647FF/Test-Baker-Bikini-Atoll-underwater-nuclear-explosion-July-25-1946.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/362098/283506"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/60/231260-050-F8D647FF/Test-Baker-Bikini-Atoll-underwater-nuclear-explosion-July-25-1946.jpg?w=300"><img src="https://cdn.britannica.com/60/231260-050-F8D647FF/Test-Baker-Bikini-Atoll-underwater-nuclear-explosion-July-25-1946.jpg?w=300" alt="Operation Crossroads" data-width="1600" data-height="1139" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/60/231260-050-F8D647FF/Test-Baker-Bikini-Atoll-underwater-nuclear-explosion-July-25-1946.jpg" data-href="/media/1/362098/283506">Operation Crossroads</a><span>“Baker,” the world's first underwater nuclear test, conducted at Bikini atoll on July 25, 1946.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">The second test, “Baker,” took place on July 25, 1946. A 23-kiloton device was suspended at a depth of 90 feet (27 meters) from a decommissioned <a href="https://www.britannica.com/technology/landing-craft" class="md-crosslink " data-show-preview="true">landing craft</a> in the Bikini lagoon. At the moment of the explosion, a luminous dome rose on the surface of the lagoon, followed by an <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="opaque" href="https://www.merriam-webster.com/dictionary/opaque" data-type="MW">opaque</a> cloud that enveloped about half the target area. The cloud dissipated within seconds, revealing a column of ascending water that lifted the 26,000-ton <a href="https://www.britannica.com/technology/battleship-naval-ship" class="md-crosslink " data-show-preview="true">battleship</a> USS <em>Arkansas</em> into the air for a brief moment. The column of water, some 2,200 feet (670 meters) in diameter, rose to a height of 1 mile (1.6 km), sending spray still higher. The expanding column of spray engulfed about half the ships in the target fleet with radioactive water. Waves traveling outward from the explosion were up to 100 feet (30 meters) tall, even at a distance of 1,000 feet (some 300 meters) from the <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="epicenter" href="https://www.britannica.com/dictionary/epicenter" data-type="EB">epicenter</a>. The evaluation board of the <a href="https://www.britannica.com/topic/Joint-Chiefs-of-Staff" class="md-crosslink " data-show-preview="true">Joint Chiefs of Staff</a> reported that the explosion had produced intense radioactivity in the waters of the lagoon. The target ships were saturated with radioactive water so lethal that four days after the test, it was still unsafe for inspection parties to spend “any useful length of time” in the center of the target area or on any of the ships anchored there. Persistent radiation and the difficulty of decontamination led to the cancellation of “Charlie,” a planned third test that would have involved a bomb being detonated at the bottom of the Bikini lagoon.</p><div class="one-good-fact-module"> </div><span class="marker MOD17 mod-inline"></span> <span class="marker PREMOD18 mod-inline"></span><p class="topic-paragraph">After the <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="conclusion" href="https://www.britannica.com/dictionary/conclusion" data-type="EB">conclusion</a> of Operation Crossroads, the Manhattan District relinquished direction of the plants and laboratories under its jurisdiction to the U.S. <a href="https://www.britannica.com/topic/Atomic-Energy-Commission-United-States-organization" class="md-crosslink " data-show-preview="true">Atomic Energy Commission</a> (AEC), a civilian agency established by act of <a href="https://www.britannica.com/topic/Congress-of-the-United-States" class="md-crosslink " data-show-preview="true">Congress</a> in August 1946. Under the AEC, weapon development and testing continued along with development of the peaceful uses of <a href="https://www.britannica.com/science/nuclear-energy" class="md-crosslink autoxref " data-show-preview="true">atomic energy</a>. The U.S. government disbanded the AEC under the Energy Reorganization Act of 1974 and divided its functions between two new agencies: the <a href="https://www.britannica.com/topic/Nuclear-Regulatory-Commission" class="md-crosslink " data-show-preview="true">Nuclear Regulatory Commission</a>, which regulates the <a href="https://www.britannica.com/technology/nuclear-power" class="md-crosslink autoxref " data-show-preview="true">nuclear power</a> industry, and the Energy Research and Development Administration, which was eliminated in 1977 when the <a href="https://www.britannica.com/topic/US-Department-of-Energy" class="md-crosslink " data-show-preview="true">Department of Energy</a> was created.</p><span class="marker MOD18 mod-inline"></span> </section> <span class="md-signature"><a href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419">The Editors of Encyclopaedia Britannica</a></span> <span class="md-signature">This article was most recently revised and updated by <a href="/editor/Erik-Gregersen/6723">Erik Gregersen</a>.</span><span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-root"></div> </div> </div> </div> <div class="ai-dialog-placeholder"></div> </div> </div> <aside class="col-md-da-320"></aside> </div> </div> </div> </div> </article></div> </div></div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <script type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Topic","templateName":"DESKTOP","pageNumber":1,"pagesTotal":1,"pageId":362098,"pageLength":2207,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-130/js/libs/jquery-3.5.0.min.js?v=3.130.14"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-130/dist/topic-page.js?v=3.130.14' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"D","adLeg":"D","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"LARGE","gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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