U.S. Department of Defense (DoD)

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</span> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/topic/US-Department-of-Defense/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/US-Department-of-Defense">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/topic/US-Department-of-Defense/images-videos">Images</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/42/78042-050-4DBEAFA9/Pentagon-headquarters-US-Department-of-Defense-Virginia.jpg" data-href="/media/1/155681/96823" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" 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<img loading="lazy" src="https://cdn.britannica.com/08/182608-004-FA323F03/headquarters-National-Reconnaissance-Office-Chantilly-Virginia.jpg" alt="National Reconnaissance Office" height="50" /> </a> <a href="https://cdn.britannica.com/00/150000-050-88189A7C/US-Army-Corps-of-Engineers-floodgates-flow-May-2011.jpg" data-href="/media/1/155681/216213" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/00/150000-004-10379BB5/US-Army-Corps-of-Engineers-floodgates-flow-May-2011.jpg" alt="U.S. Army Corps of Engineers" height="50" /> </a> <a href="https://cdn.britannica.com/75/178775-050-096BCE62/insignias-military-officers.jpg" data-href="/media/1/155681/199826" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/75/178775-004-0B6F3CBA/insignias-military-officers.jpg" alt="military rank insignias" height="50" /> </a> </div> <button disabled class="prev-button js-prev-button position-absolute btn 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data-asm-type="image"> <div class="md-assembly-wrapper card-media " data-type="image"> <a style="min-height: 160px;" href="https://cdn.britannica.com/42/78042-050-4DBEAFA9/Pentagon-headquarters-US-Department-of-Defense-Virginia.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/155681/96823"> <picture> <source media="(min-width: 680px)" srcset="https://cdn.britannica.com/42/78042-050-4DBEAFA9/Pentagon-headquarters-US-Department-of-Defense-Virginia.jpg?w=300"> <img src="https://cdn.britannica.com/42/78042-050-4DBEAFA9/Pentagon-headquarters-US-Department-of-Defense-Virginia.jpg?w=400&h=300&c=crop" alt="the Pentagon" 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/42/78042-050-4DBEAFA9/Pentagon-headquarters-US-Department-of-Defense-Virginia.jpg" data-href="/media/1/155681/96823">the Pentagon</a> <span><span>The Pentagon, headquarters of the U.S. Department of Defense, Arlington county, Virginia.</span></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="topic-header"> <div class="d-flex align-items-top justify-content-between"> <div class="d-flex flex-column"> <div> <div> <h1>U.S. Department of Defense</h1></div> </div> <div class="topic-identifier font-16 font-md-20">United States government</div> </div> </div> <div class="d-none d-sm-flex 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Let us know if you have suggestions to improve this article (requires login). </div> <div class="type-menu"> <label for="feedback-type" class="label mb-10">Feedback Type</label> <select id="feedback-type" class="form-select mb-30" name="feedbackTypeId" required> <option value="" selected="selected">Select a type (Required)</option> <option value="1">Factual Correction</option> <option value="2">Spelling/Grammar Correction</option> <option value="3">Link Correction</option> <option value="4">Additional Information</option> <option value="5">Other</option> </select> </div> <label for="feedback" class="label mb-10">Your Feedback</label> <textarea id="feedback" class="form-control mb-30" name="feedback" maxlength="3000" rows="7" required></textarea> <button class="btn btn-blue" type="submit">Submit Feedback</button> </form> <div class="success-messaging d-none mt-30"> <div class="title">Thank you for your feedback</div> <p>Our editors will review what you’ve submitted and determine whether to revise the article.</p> </div> </div> </div> <div class="md-websites-modal size-lg d-none"> <div class="md-modal-body"> <div class="h2 font-serif pb-15 border-bottom font-weight-bold"> External Websites </div> <div class="pb-20"> <ul class="list-unstyled mt-20 lh-lg"> <li><a class="external" href="https://www.defense.gov/" target="_blank" rel="noopener nofollow">Official Site of the United States Department of Defense</a></li> </ul> </div> </div> </div> </div> </div> <div class="toc-header-marker"></div> <button class="ai-ask-button btn border-2 js-header-ai-ask-button d-none btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10"> Ask the Chatbot a Question </button> <div class="caption alternate-titles">Also known as: DOD</div> <div class="md-byline module-spacing "> <div class="font-serif font-12"> <span class="written-by text-gray-700"> Written and fact-checked by </span> <div class="editor-popover popover p-0"> <a class="d-block p-20 gtm-byline font-12 byline-contributor" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. 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="2024-11-28T00:00:00CST" >Nov 28, 2024</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/topic/US-Department-of-Defense/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>1947 - present</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>Areas Of Involvement: </dt> <dd><a href="/topic/national-security">national security</a></dd> <dd><a href="/topic/defense-national-defense">defense</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>Related People: </dt> <dd><a href="/biography/James-Mattis">James Mattis</a></dd> <dd><a href="/biography/Robert-M-Gates">Robert M. 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Trump’s defense pick reignites the debate</a> <span class="font-14 text-gray-600"> <span>•</span> Nov. 18, 2024, 1:45 PM ET (AP) </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="ref1025974"></span>U.S. Department of Defense (DoD)</strong>, executive division of the U.S. federal government responsible for ensuring national security and supervising U.S. military forces. Based in the <a href="https://www.britannica.com/topic/Pentagon" class="md-crosslink " data-show-preview="true">Pentagon</a>, it includes the <a href="https://www.britannica.com/topic/Joint-Chiefs-of-Staff" class="md-crosslink " data-show-preview="true">Joint Chiefs of Staff</a>, the departments of the <a href="https://www.britannica.com/topic/The-United-States-Army" class="md-crosslink " data-show-preview="true">U.S. Army</a>, <a href="https://www.britannica.com/topic/The-United-States-Navy" class="md-crosslink " data-show-preview="true">U.S. Navy</a>, and <a href="https://www.britannica.com/topic/The-United-States-Air-Force" class="md-crosslink " data-show-preview="true">U.S. Air Force</a>, and numerous defense agencies and allied services. It was formed in 1947 by an act of <a href="https://www.britannica.com/topic/Congress-of-the-United-States" class="md-crosslink " data-show-preview="true">Congress</a> (amended 1949) <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="combining" href="https://www.britannica.com/dictionary/combining" data-type="EB">combining</a> the War and Navy Departments.</p><span class="marker MOD1 mod-inline"></span><span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">The mission of the Department of Defense is to provide, through its military strength, a solid foundation for the national policy of the <a href="https://www.britannica.com/place/United-States" class="md-crosslink autoxref " data-show-preview="true">United States</a>. The forerunner of the Department of Defense, the National Military Establishment, was created by the <a href="https://www.britannica.com/topic/National-Security-Act" class="md-crosslink autoxref " data-show-preview="true">National Security Act</a> of 1947 and evolved from the experiences of <a href="https://www.britannica.com/event/World-War-II" class="md-crosslink " data-show-preview="true">World War II</a>. While combat and service components of the Departments of the Army and the Navy fought together in various theatres of operation under unified direction of overseas commanders, the individual military departments reported separately to the president. The conflicting and competitive policies of these departments prevented a truly effective, coordinated, and unified military effort. To overcome this organizational deficiency, the National Military Establishment was created, and the <a href="https://www.britannica.com/topic/cabinet-government#ref284371" class="md-crosslink " data-show-preview="true">cabinet</a> post of secretary of defense was established to provide overall policy and direction of the military departments without destroying their individual identities. Concurrently, the Air Force was created as a third military department on a coequal basis with the Departments of the Army and the Navy.</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="215924" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/22/180522-050-2591413D/Pres-Harry-S-Truman-National-Security-Act-1947.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/155681/215924"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/22/180522-050-2591413D/Pres-Harry-S-Truman-National-Security-Act-1947.jpg?w=300"><img src="https://cdn.britannica.com/22/180522-050-2591413D/Pres-Harry-S-Truman-National-Security-Act-1947.jpg?w=300" alt="National Security Act of 1947" data-width="1600" data-height="1081" 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/22/180522-050-2591413D/Pres-Harry-S-Truman-National-Security-Act-1947.jpg" data-href="/media/1/155681/215924">National Security Act of 1947</a><span>U.S. Pres. Harry S. Truman signing the National Security Act of 1947.</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 original National Security Act of 1947 provided the secretary of defense with limited authority and staff to exercise control. However, subsequent <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="amendments" href="https://www.merriam-webster.com/dictionary/amendments" data-type="MW">amendments</a> to the basic act in 1949, 1953, and 1958 greatly strengthened the authority and ability of the secretary to direct defense policy. With the 1949 <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="amendment" href="https://www.merriam-webster.com/dictionary/amendment" data-type="MW">amendment</a>, the modern Department of Defense was established. In the early 21st century the Department of Defense consisted of the secretary of defense; the deputy secretary of defense; undersecretaries and assistant secretaries holding various portfolios; the office of the inspector general; the Departments of the Army, Navy, and Air Force; and numerous defense agencies and field activity offices. These civilian officials and their subordinates represent the policy, research, analysis, and resource-management staff of the secretary of defense.</p><div class="module-spacing"> </div><span class="marker MOD3 mod-inline"></span><span class="marker PREMOD4 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="107573" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/56/103056-050-8D47C077/Tommy-Franks-Donald-Rumsfeld-Central-Command-2002.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/155681/107573"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/56/103056-050-8D47C077/Tommy-Franks-Donald-Rumsfeld-Central-Command-2002.jpg?w=300"><img src="https://cdn.britannica.com/56/103056-050-8D47C077/Tommy-Franks-Donald-Rumsfeld-Central-Command-2002.jpg?w=300" alt="Tommy Franks and Donald Rumsfeld" data-width="1600" data-height="1082" 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/56/103056-050-8D47C077/Tommy-Franks-Donald-Rumsfeld-Central-Command-2002.jpg" data-href="/media/1/155681/107573">Tommy Franks and Donald Rumsfeld</a><span>Gen. Tommy Franks (left), commander in chief of Central Command, with U.S. Secretary of Defense Donald Rumsfeld, 2002.</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 civilian secretaries of the military departments (Army, Navy, and Air Force) are responsible for the administration of their particular departments and are responsible for training, equipping, and providing combat-ready forces to the combat commands. The combat forces of the Army, Navy, Air Force, and Marine <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> are under unified combat commands, organized on either a geographic or a functional basis. A unified command contains combat forces from more than one service, such as Central Command (CENTCOM), which is composed of all Army, Navy, Air Force, and Marine Corps units in Central and Southern Asia and the <a href="https://www.britannica.com/place/Middle-East" class="md-crosslink autoxref " data-show-preview="true">Middle East</a>, or Special Operations Command (USSOCOM), which oversees <a href="https://www.britannica.com/topic/special-operations-warfare" class="md-crosslink " data-show-preview="true">special operations warfare</a>.</p><span class="marker MOD4 mod-inline"></span><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="216409" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/71/146871-050-39575688/Pres-meeting-Barack-Obama-repeal-Oval-Office-November-29-2010.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/155681/216409"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/71/146871-050-39575688/Pres-meeting-Barack-Obama-repeal-Oval-Office-November-29-2010.jpg?w=300"><img src="https://cdn.britannica.com/71/146871-050-39575688/Pres-meeting-Barack-Obama-repeal-Oval-Office-November-29-2010.jpg?w=300" alt="Joint Chiefs of Staff" data-width="1600" data-height="1067" 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/71/146871-050-39575688/Pres-meeting-Barack-Obama-repeal-Oval-Office-November-29-2010.jpg" data-href="/media/1/155681/216409">Joint Chiefs of Staff</a><span>Pres. Barack Obama (his back to the camera) holding a meeting with the Joint Chiefs of Staff in the Oval Office concerning the repeal of "Don't Ask, Don't Tell," November 29, 2010.</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 commanders of the unified commands are responsible to the president and the secretary of defense. By secretarial delegation, the Joint Chiefs of Staff exercise operational direction over the unified commands. The Joint Chiefs of Staff are the principal military advisers to the president, the <a href="https://www.britannica.com/topic/National-Security-Council-United-States-agency" class="md-crosslink autoxref " data-show-preview="true">National Security Council</a>, and the secretary of defense. The Joint Chiefs of Staff consist of the chairman, Joint Chiefs of Staff, who is the nation’s highest-ranking military officer; the vice chairman; the chief of staff, United States Army; the chief of naval operations; the chief of staff, U.S. Air Force; the commandant of the Marine Corps; and the chief of the National Guard. The chiefs are appointed by the president to four-year terms. The Joint Chiefs of Staff are supported by the Joint Staff, which is limited by law to not more than 400 officers. This staff is organized along <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="conventional" href="https://www.britannica.com/dictionary/conventional" data-type="EB">conventional</a> military staff lines, and performs such functions as developing strategic concepts and war plans, reviewing the operating plans of the unified commands, and establishing unified doctrine for operations. An assignment to the Joint Staff provides military officers a unique opportunity to work on coordinated plans and to develop an understanding of the <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="integrated" href="https://www.merriam-webster.com/dictionary/integrated" data-type="MW">integrated</a> effort required under the modern concept of joint operations.</p><span class="marker MOD5 mod-inline"></span><span class="marker PREMOD6 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="216410" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/07/182607-050-9F86E51F/headquarters-National-Security-Agency-Fort-Meade-Maryland.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/155681/216410"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/07/182607-050-9F86E51F/headquarters-National-Security-Agency-Fort-Meade-Maryland.jpg?w=300"><img src="https://cdn.britannica.com/07/182607-050-9F86E51F/headquarters-National-Security-Agency-Fort-Meade-Maryland.jpg?w=300" alt="National Security Agency" data-width="1600" data-height="1067" 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/07/182607-050-9F86E51F/headquarters-National-Security-Agency-Fort-Meade-Maryland.jpg" data-href="/media/1/155681/216410">National Security Agency</a><span>National Security Agency headquarters, Fort Meade, Maryland.</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="216411" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/08/182608-050-777A2BF4/headquarters-National-Reconnaissance-Office-Chantilly-Virginia.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/155681/216411"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/08/182608-050-777A2BF4/headquarters-National-Reconnaissance-Office-Chantilly-Virginia.jpg?w=300"><img src="https://cdn.britannica.com/08/182608-050-777A2BF4/headquarters-National-Reconnaissance-Office-Chantilly-Virginia.jpg?w=300" alt="National Reconnaissance Office" data-width="1600" data-height="1067" loading="eager"></picture><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">2 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/08/182608-050-777A2BF4/headquarters-National-Reconnaissance-Office-Chantilly-Virginia.jpg" data-href="/media/1/155681/216411">National Reconnaissance Office</a><span>National Reconnaissance Office headquarters in Chantilly, Virginia.</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></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">In the early 21st century there were 20 defense agencies within the Department of Defense. These agencies were established to provide integrated and unified effort in support activities that generally cut across service lines. The defense agencies have consolidated functions that were previously fractionalized among the military services. Among these agencies were the <a href="https://www.britannica.com/topic/National-Security-Agency" class="md-crosslink " data-show-preview="true">National Security Agency</a> (NSA), which held responsibility for signals intelligence and <a href="https://www.britannica.com/topic/cryptography" class="md-crosslink " data-show-preview="true">cryptography</a>; the <a href="https://www.britannica.com/topic/Defense-Advanced-Research-Projects-Agency" class="md-crosslink " data-show-preview="true">Defense Advanced Research Projects Agency</a> (DARPA), responsible for military research and development; the <a href="https://www.britannica.com/topic/Defense-Intelligence-Agency" class="md-crosslink autoxref " data-show-preview="true">Defense Intelligence Agency</a> (DIA), responsible for military <a href="https://www.britannica.com/topic/intelligence-international-relations" class="md-crosslink " data-show-preview="true">intelligence</a>; and the National Reconnaissance Office, which designs and maintains reconnaissance <a href="https://www.britannica.com/technology/Earth-satellite" class="md-crosslink " data-show-preview="true">satellites</a> for use by the Department of Defense and the intelligence <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="community" href="https://www.merriam-webster.com/dictionary/community" data-type="MW">community</a>.</p><span class="marker MOD6 mod-inline"></span><span class="marker PREMOD7 mod-inline"></span><p class="topic-paragraph">The need for the military to consider implications of political, economic, and scientific factors in the development of military plans and military advice requires that senior military officers have a broad education in these disciplines. To this end, the military departments have established an extensive continuing education system for their officers. Included in this educational system are joint-service schools such as the Joint Forces Staff College and <a href="https://www.britannica.com/topic/National-Defense-University" class="md-crosslink " data-show-preview="true">National Defense University</a>, as well as individual service schools such as the Naval War College, Air University, and Army War College. These schools offer graduate school-level programs to train future military leaders as broadly educated officers who understand the importance of political, economic, and scientific factors on military planning.</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; 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