U.S. Department of Defense

Established in 1949 and the oldest and largest government agency, the U.S. Department of Defense (DoD) works to provide the needed forces and technologies to deter war and protect the security of the United States. The department's priorities are: to increase the lethality of the United States Armed Forces, to strengthen existing alliances and attract new alliances, and to reform the department.

The organization is headed by the Secretary of Defense, the office of which is held by Lloyd J. Austin III as of February 2021. It employs over 1.4 million active duty service members, 1.1. million National Guard and Reserve forces, and 718,000 civilian personnel. Their yearly budget is around $716 billion, about 3.1% of the United States Gross Domestic Product. The U.S. Department of Defense is headquartered at the Pentagon, at Arlington, Virginia and near Washington, D.C. They have a presence in more than 160 countries, with approximately 4,800 defense sites.

Organization of the Department of Defense

The Secretary of Defense is the leader and chief executive officer of the United States Department of Defense. The position is of command and authority over the military, which is second only to the president. The position is appointed by the president with the advice and consent of the Senate, and is by custom a member of the Cabinet and by law a member of the National Security Council. Subject only to the orders of the president, the Secretary of Defense exercises command and control for administrative and operational purposes over all service branches administered by the Department of Defense.

Organization of the Office of the Secretary of Defense

Under Title 10 of the U.S. Code, the secretary of defense is the principal advisor to the president on defense matters and all matters relating to the Department of Defense. The position is a cabinet position, and as the head of an executive department is considered to be the chief executive officer of the branch and is given authority, direction, and control over the Department of Defense. Per Title 10, the chain of command follows the president to the secretary of defense, and from the secretary of defense to the commander of the combatant commands.

The Secretary of Defense manages the Department of Defense through a combination of direction from the president and Congress; the latter directs through statute and laws. As well, the subordinate positions of the Principal Staff Assistants, Joint Chiefs of Staff, and the heads of the DoD components provide advice and support to the Secretary of Defense. The advice and decision making process inside the DoD can include delegations of authority and authorities provided by the law—to intra-governmental advisory bodies, to Federal Advisory Committee Act (FACA) advisory bodies, and to external advisory bodies from the private sector. The private sector bodies are closely regulated by statute to prevent conflicts of interest.

The Joint Chiefs of Staff is a body of senior uniformed leaders within the United States Department of Defense. The group is responsible for advising the president, the secretary of defense, the Homeland Security Council, and the National Security Council on military matters. The composition of the Joint Chiefs of Staff is defined by statute and consists of a chairman, a vice chairman, the service chiefs of the Army, Marine Corps, Navy, Air Force, Space Force, and the chief of the National Guard Bureau. Each service chief works under the secretaries of their respective military departments beyond their Joint Chiefs of Staff obligations.

Organization of the Joint Chiefs of Staff

The chairman of the Joint Chiefs of Staff is the United States' highest-ranking military officer, who is supported by the vice chairman. Other positions include the Chief of Staff of the United States Army, the Chief of Naval Operations, the Chief of Staff of the United States Air Force, the commandant of the Marine Corps, and the Chief of the National Guard. These chiefs are appointed by the president to four year terms. The Joint Chiefs of Staff is supported by the Joint Staff, which is limited by law to not more than 400 officers. This staff is organized along conventional military 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.

The Army, Navy, Air Force, and Marine Corps are under unified combat commands, organized either on 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 Middle East, or Special Operations Command (USSOCOM), which oversees special operations warfare. The other unified commands include:

• U.S. Northern Command (USNORTHCOM)
• U.S. Southern Command (USSOUTHCOM)
• U.S. Central Command (USCENTCOM)
• U.S. European Command (USEUCOM)
• U.S. Indo-Pacific Command (USINDOPACOM)
• U.S. African Command (USAFRICOM)
• U.S. Strategic Command (USSTRATCOM)
• U.S. Special Operations Command (USSOCOM)
• U.S. Transportation Command (USTRANSCOM)
• U.S. Cyber Command (USCYBERCOM)
• U.S. Space Command (USSPACECOM)

Unified commands areas of responsibility.

The commanders of the unified commands are responsible to the president and secretary of defense. By secretarial delegation, the Joint Chiefs of Staff exercises operational direction over the unified commands.

The U.S. Department of Defense has three subordinate military departments: the Department of the Army, the Department of the Navy, and the Department of the Air Force. They also have four subordinate intelligence services, including: the Defense Intelligence Agency (DIA), the National Security Agency (NSA), the National Geospatial-Intelligence Agency (NGA), and the National Reconnaissance Office (NRO). Other defense agencies include:

• The Defense Advanced Research Projects Agency (DARPA)
• The Strategic Capabilities Office (SCO)
• The Defense Logistics Agency (DLA)
• The Missile Defense Agency (MDA), the Defense Health Agency (DHA)
• The Defense Threat Reduction Agency (DTRA)
• The Defense Counterintelligence and Security Agency
• The Pentagon Force Protection Agency (PFPA)

These defense agencies were established and consolidated to provide integrated and unified support activities across service lines. Many of these functions were originally done within the different military services until the Department of Defense consolidated them under divisions, such as the National Security Agency, which holds responsibility for signals for intelligence and cryptography; the Defense Advanced Research Projects Agency, which consolidates responsibilities for military research and development; the Defense Intelligence Agency, which holds responsibility for military intelligence; and the National Reconnaissance Office, which designs and maintains reconnaissance satellites for use by the Department of Defense, the divisions within the DoD, and the intelligence community.

Emblem of the Department of the Army

The United States Department of the Army is one of the three military departments within the Department of Defense. The Department of the Army is the federal government agency within the United States Army and is led by the Secretary of the Army. The Secretary of the Army is a civilian position, which is appointed by the president and with confirmation by the United States Senate. Responsible for, and with the authority to conduct the affairs of the Department of the Army, the Secretary of the Army is subject to the authority, direction and control of the secretary of defense. The Department of the Army is responsible for the assignation of Army forces, operational command of the commanders of combatant commands, and the duties enumerated in 10 U.S.C., which includes the organization, training, and equipping of the Army forces.

The Department of the Army, through its Corp of Engineers, performs important civil functions in improving rivers, harbors, and waterways for navigation, in constructing flood control and similar projects in various parts of the country, and in administering the laws governing navigable waters.

Emblem of the Department of the Navy

The United States Department of the Navy is one of the three military departments within the Department of Defense. The Department of the Navy was established on April 30, 1798 through an Act of Congress to provide structure to the United States Navy, the United States Marine Corps, and the United States Coast Guard. The head of the Department of the Navy is the Secretary of the Navy. Before amendments in 1949 to the National Security Act of 1947, the Secretary of the Navy was a member of the president's cabinet, but since 1949 the amendment the Secretary of the Navy serves on the Joint Chiefs of Staff.

Emblem of the Department of the Air Force

The United States Department of the Air Force is one of the three military departments within the Department of Defense. Formed on September 18, 1947, per the National Security Act of 1947, the Department of the Air Force is the military department that houses the United States Air Force and the United States Space Force. The Secretary of the Air Force heads the Department of the Air Force. A civilian position, the Secretary of the Air Force is responsible for, and has the authority for, conducting the affairs of the Department of the Air Force, and is subject to the authority, direction, and control of the Secretary of Defense.

Emblem of the United States Army

The land service branch of the United States Armed forces, the United States Army is one of the uniformed services of the Department of Defense and is designated as the Army of the United States in the U.S. Constitution. The Army is the oldest and most senior branch of the U.S. military in order of precedence. The United States army is part of the Department of the Army, and is headed by the secretary of the Army—a senior-appointed civilian service, and by the chief of staff of the Army—a member of the Joint Chiefs of Staff.

Emblem of the United States Navy

The United States Navy is the maritime branch of the United States Armed Forces and the Department of Defense. The United States Navy is the largest navy in the world, with the estimated tonnage of its active battle fleet estimated to exceed the next thirteen navies combined. The U.S. Navy originated with the Continental Navy, established during the American Revolutionary War. The U.S. Congress passed the Naval Act of 1794 for the construction of six heavy frigates, the first ships of the U.S. Navy. The U.S. Navy is part of the Department of the Navy, along with the U.S. Marine Corps (the U.S. Navy's coequal sister service). The most senior officer of the U.S. Navy is the Chief of Naval Operations, who serves the Department of the Navy and the Secretary of the Navy.

Emblem of the United States Marine Corps

The United States Marine Corps (USMC), also known as the United States Marines, is the maritime land service branch of the United States Armed Forces and the Department of Defense. The USMC is responsible for expeditionary and amphibious operations through combined arms, and implements its own infantry, armor, artillery, aerial, and special operations forces. The USMC is part of the U.S. Department of the Navy, and operates on land and aboard sea-going amphibious warfare ships around the world. This includes tactical aviation squadrons that are also embedded in Navy carrier air wings and operate from the aircraft carriers.

Emblem of the United States Air Force

The United States Air Force (USAF) is the air service branch of the United States Armed Forces and the Department of Defense. The USAF was formed as part of the United States Army on August 1, 1907, and was formally established as a separate branch on September 18, 1947, as per the National Security Act of 1947. The USAF's core missions are air superiority, global integrated intelligence, surveillance and reconnaissance, rapid global mobility, global strike, and command and control. The USAF is headed by the Secretary of the Air Force as a division of the Department of the Air Force. The highest-ranking military officer in the USAF is the Chief of Staff of the Air Force. Along with independent air operations, the USAF provides air support for land and naval forces.

Emblem of the United States Coast Guard

The United States Coast Guard is the maritime security, search and rescue, and law enforcement branch of the United States Armed Forces and the Department of Defense. The Coast Guard is a maritime, military, and multi-mission service that includes maritime law enforcement in both domestic and international waters and a federal regulatory agency. The Coast Guard was created by the U.S. Congress in August 4, 1790 at the request of Alexander Hamilton. It is the oldest continuous seagoing service in the United States. During peacetime, the U.S. Coast Guard operates under the U.S. Department of Homeland Security and is transferred to the U.S. Department of the Navy under the Department of Defense at any time by the president, or else by the U.S. Congress during wartime.

Emblem of the United States Space Force

The United States Space Force is the space service branch of the U.S. Armed Forces and the Department of Defense. The Space Force is the first independent space force and the sister-branch of the U.S. Air Force under the Department of the Air Force. The systems and spacecraft of the Space Force include the Global Positioning System constellation, the military satellite communications constellations, the Boeing X-37B spaceplane, the U.S. missile warning system, the U.S. space surveillance network, and the Satellite Control Network. The Space Force is responsible for organizing, training, and equipping space forces, which are further presented to the unified combatant commands.

Part of the functions of the Department of Defense is intelligence gathering in order to support policy decisions and wartime operations. There are nine intelligence service divisions within the DoD, which include four individual intelligence services and the five intelligence services of the major departments of the DoD.

Defense Intelligence Agency badge.

The Defense Intelligence Agency (DIA) is a Department of Defense combat support agency. The DIA is a producer and manager of foreign military intelligence and provides military intelligence to warfighters, defense policymakers, and force planners in the DoD and in the Intelligence Community. The DIA is also engaged in military planning and operations and weapon systems acquisition. The director of the DIA serves as a principal adviser to the secretary of defense and to the chairman of the Joint Chiefs of Staff on matters of military intelligence.

National Security Agency badge.

The National Security Agency (NSA), or Central Security Service, is the United States' cryptologic organization that coordinates, directs, and performs specialized activities to protect the information systems that produce foreign signals information. Founded in 1952, the NSA is part of the DoD and a member of the U.S. Intelligence Community. The organization focuses on developing and maintaining technologies and working at the forefront of the communications and information technology trends, while also working as an important center for foreign language analysis and research within the United States government. The NSA is suggested to be the largest employer of mathematicians in the United States.

National Geospatial-Intelligence Agency badge.

The National Geospatial-Intelligence Agency (NGA) is a geospatial intelligence service supporting national security objectives. The information collected and processed by the NGA is tailored for customer-specific solutions, whether those customers are members of the DoD, the United States government, or customers in private industry. Through the ready access to geospatial access, the NGA provides support to civilian and military leaders and the United States military forces state of readiness. NGA also contributes to humanitarian efforts, such as tracking floods and fires and peacekeeping.

National Reconnaissance Office badge.

The National Reconnaissance Office (NRO) is a designer, builder, and operator of the United States' reconnaissance satellites. NRO's products, which are provided to customers like the Central Intelligence Agency, can warn of potential trouble spots around the world, help plan for military operations, and monitor the environment. Even though the NRO is a DoD office, the division is staffed by DoD and CIA personnel and is funded through the National Reconnaissance Program and part of the National Foreign Intelligence Program.

The Air Force Intelligence, Surveillance, and Reconnaissance (USAF ISR) is a provider of intelligence derived from airborne, space, and cyberspace sensors. The USAF ISR works to deliver intelligence for decision advantage for commanders to achieve kinetic and non-kinetic effects on targets globally, and to support national, strategic, operational, and tactical requirements. USAF ISR is included in oversight of planning, programming, budgeting, developing and implementing Air Force policies, and guiding Air Force global integrated ISR activities.

The Army Intelligence (G-2), similar to the USAF ISR, is the branch of intelligence for the Army division and is responsible for policy formulation, planning, programming, budgeting, management, staff supervision, evaluation, and oversight for intelligence activities for the Department of Army. Army Intelligence is responsible for overall coordination of the five major military intelligence disciplines:

• Imagery intelligence
• Signals intelligence
• Human intelligence
• Measurement and signals intelligence
• Counterintelligence and security countermeasures

The U.S. Marine Corps Intelligence is an intelligence arm of the Marine Corps and produces tactical and operational intelligence for battlefield support. The Marine Corps Intelligence is responsible for policy, plans, programming, budgets, and staff supervision of intelligence and supporting activities within the USMC. The department supports the commandant of the Marine Corps in their role as a member of the Joint Chiefs of Staff, represents the service in Joint and Intelligence Community matters, and exercises supervision over the Marine Corps Intelligence Activity. The department has responsibility for geospatial intelligence and counterintelligence, and ensures synchronized strategies for the development of ISR activities.

The Navy Intelligence, under the direction of the Director of Naval Intelligence, is a provider of maritime intelligence to the Navy and joint or combined warfighting forces, as well as to decision makers and other partners or consumers in the United States intelligence community.

The United States Space Force (USSF) was established on December 20, 2019 and is the newest branch of the Armed Forces. The USSF was initially established within the department of the Air Force, and under the guidance of the Secretary of Defense and with the Secretary of the Air Force having overall responsibility for the USSF. The growing intelligence group within the USSF is led by the Chief of Space Operations and provides intelligence to the growing USSF.

The Department of Defense is a federally funded department of the executive branch of the United States government. The funds for the Department of Defense are part of the federal budget and the allocation of those funds are at the discretion of the secretary of defense. For the FY 2021, the DoD's base budget is around $636 billion, which is larger than the budgets for ExxonMobil or Walmart. The DOD budget is far greater than the next two largest government agencies—in comparison, the Department of Health and Human Services had a 2021 budget request of $94.5 billion and the Department of Veteran Affairs had a $105 billion request.

The 2021 DoD budget funds the creation of the United States Space Force, the United States Space Command, and the Space Development Agency. The budget also allocates $9.8 billion on cyberspace strategy and expansion of artificial intelligence. And the budget aims to build a new missile field at Fort Greely, Alaska, with twenty silos and twenty additional Ground-Based Interceptors, for the purpose of defending against missile threats from North Korea, among other countries.

In the base requests of the 2021 Defense Budget, the Department of the Air Force receives around 29% of the total budget, the Department of the Navy receives about 30% of the total budget, and the Department of the Army receives around 24% of the budget. Defense-wide allocations comprise the remainder of the balance. A large portion of the defense budget goes to contractors. In 2018, the Congressional Research Services performed a study that found defense contracts accounted for $320 billion of the federal government's total $507 billion contract obligations for the fiscal year 2017 budget.

The DoD budgets are for direct expenditures to support the department's day-to-day operations. War costs are paid out of an Overseas Contingency Operations fund. In 2021, this budget was at $69 billion.

In 2019, a department-wide audit reported that the Department of Defense had $2.9 trillion in assets and $2.8 trillion in liabilities. About one-fourth of the DoD's assets consisted of plants, equipment, and inventory. In 2017, the National Defense Authorization Act stated that climate change is a "direct threat" to these assets. Extreme weather, rising sea levels, and flooding as a result of global warming is expected to endanger 128 military bases, and as a result Congress asked the DoD to identify the ten most vulnerable sites and recommend strategies and solutions. In January 2019, the DoD reported on the seventy nine installations most at risk, and cited recurrent flooding at fifty three bases, drought at forty three installations, and threat of wildfires at thirty six sites. So far, the DoD has developed coping solutions and strategies to address these problems.

In FY 2019, the DoD listed 94% of the department's liabilities as retirement and employment benefits. It had $607.6 billion in Treasury securities and $1.19 trillion in other investments. The amount is not considered enough to cover the possible $2.76 trillion in future retirement and medical benefits for veterans. Retirement benefits cost the DoD $206 billion in 2019.

On November 15, 2018, Ernst & Young and other private firms were hired to audit the Department of Defense on behalf of Congress. The firms announced they were unable to complete the job. The DoD is estimated to receive close to 54 cents out of each dollar in federal appropriations but had, previous to 2018, not audited itself for decades. The firms concluded the DoD's financial irregularities, bookkeeping deficiencies, and errors that a reliable audit was impossible. Deputy Secretary of Defense Patrick Shanahan suggested the attempt at the audit was in itself an accomplishment, as the audit was on a $2.7 trillion organization.

Part of the development of the Department of Defense and the Joint Chiefs of Staff has been the understanding of the need for military personnel and leaders to understand the implications of political, economic, and scientific factors in the development of military plans and military advice. Therefore, military officers are required to have a broad education, and to this end, the military departments have established an extensive continuing education system for their officers. Included in this system are joint-service schools, such as the Joint Forces Staff College and National Defense University. The individual services also offer schools such as the Naval War College, Air University, and Army War College. These schools offer graduate school programs to train future military leaders as broadly educated officers who understand of various factors on military planning.

There is also an Implementation of the Continuous Learning policy for the Department of Defense acquisition, technology, and logistics workforce, which applies to civilian and military personnel. The continuing education is intended to maximize DoD resources and eliminate duplication with proposed continuous learning modules from all sources.

The Department of Defense operates the Department of Defense Education Activity, or DoDEA, which operates 160 schools in eight districts located in eleven countries, seven states, and two territories. The DoDEA helps educate 996,069 military-connected children of all ages and are served by approximately 8,700 educators. All schools within the DoDEA are fully accredited by the United States accreditation agencies.

As one of only two federally-operated school systems, the DoDEA is responsible for planning, directing, coordinating, and managing prekindergarten through twelfth grade educational programs on behalf of the DoD. The DoDEA operates as a field activity of the office of the Secretary of Defense (Personnel and Readiness). The DoDEA is headed by a director who oversees all agency functions from the DoDEA headquarters in Alexandria, Virginia. The DoDEA's schools are divided into three geographic areas: Europe, the Pacific, and the Americas.

The DoDEA's beginnings were at the end of World War II, with the establishment of the Department of Defense Dependents Schools. At this time there was no precedent or establishing and operating schools in foreign occupied countries. These first schools were established in 1946 in Germany, Austria, and Japan. Within three years, there were nearly one hundred schools that were operated by the Army, Navy, and Air Force.

These independent school systems had been established and operated by the different divisions of the United States military. In the arrangement, the Army operated schools in Europe, Africa, and the Middle East. The Air Force operated schools in the Pacific, which included Japan, Okinawa, Taiwan, the Philippines, Korea, and Midway Island. The Navy operated all schools in the Atlantic, which included Iceland, Labrador, Newfoundland, Bermuda, Cuba, Eleuthera, and Antigua. In 1964, the Secretary of Defense combined the three separate school systems.

During the 1960s, worldwide enrollment in the overseas schools averaged 160,000. In 1976, a Joint House-Senate Conference Committee Report decided the Department of Defense would take over operation of the military dependent schools. The newly-established office in the Pentagon, the Office of Overseas Dependent Education, was responsible to the Deputy Assistant Secretary of Defense for Manpower and Reserve Affairs. The Office of Overseas Dependents Education became the Department of Defense Dependents Schools (DoDDS).

Following the winding down of the Cold War in the late 1980s and early 1990s, the number of DoDDS schools was reduced and combined with the United States-based Domestic Dependents Elementary and Secondary Schools (DDESS) to form the Department of Defense Education Activity in 1992. The same year saw the DoDDS headquarters in Arlington, Virginia become the Department of Defense Activity (DoDEA).

On March 4, 1789, the First United States Congress legislated to create a military defense force. This followed the establishment of the Continental Army on June 14, 1775, the Continental Navy on October 14, 1775, and the Continental Marines on November 10, during the Revolutionary War. The development of the military defense force stagnated as different governmental concerns took the focus of Congress. During this time, President George Washington went to Congress twice to remind them of their duty to establish a military. On the final day of the session, September 29, 1789, Congress created the War Department, a precursor to the Department of Defense. The War Department was responsible for handling naval affairs before the creation of the Navy Department in 1798. The secretaries of these departments reported to the president as cabinet-level advisers until 1949, when all departments of the military became subordinate to the Secretary of Defense.

President Truman during the signing of the National Security Amendment Act of 1949.

At the end of World War II, President Harry Truman proposed the creation of a unified department of national defense. The message to Congress on December 19, 1945 cited wasteful military spending and interdepartmental conflicts. Congress deliberated for months over the role of the military in society and the threat of granting too much military power to the executive branch. On July 26, 1947, Truman signed the National Security Act of 1947, which established the unified military command known as the National Military Establishment. This same act established the Central Intelligence Agency, the National Security Council, the National Security Resources Board, the United States Air Force (formerly the Air Force), and the Joint Chiefs of Staff. The act placed the National Military Establishment under control of a single secretary of defense.

Organization of the NME as of 1947

On September 18, 1947, the National Military Establishment began operations with James V. Forrestal—confirmed by the Senate as the first Secretary of Defense. On August 10, 1949, the National Military Establishment was renamed the Department of Defense and absorbed the three cabinet-level military departments in an amendment to the original 1947 law. In 1958, under the Department of Defense Reorganization Act of the same year, channels of authority within the department were streamlined while maintaining the ordinary authority of the Military Departments to organize, train, and equip their associate forces. This act further clarified the decision-making authority of the secretary of defense with respect to the subordinate military departments. The act also clearly defined the operational chain of command over U.S. military forces. Developing a centralized research authority was part of the 1958 act, the Advanced Research Projects Agency, eventually known as DARPA. The act was written and promoted by the Eisenhower administration and signed into law on August 6, 1958.

The military operations that became tantamount in the United States and Soviet competition for international dominance, also known as the Cold War, saw the DoD grow into the largest of the U.S. governmental institutions. Part of this was the arms build-up around strategic nuclear weapons.

Image of the Boeing B-52 Stratofortress.

To carry these weapons, the development of long-range bombers grew in focus, especially with the generation of jet-powered aircraft taking over air force squadrons. The long-range bomber in this perspective was the B-52 Stratofortress. Air wings comprised of B-52s, based in the U.S. and globally, were set up on round-the-clock aerial missions to fly toward the Soviet Union until reaching a "fail safe" point at which they turned around unless given the "go codes" from Strategic Air Command.

The overall commitment to the continual arms manufacturing or procurement led, in part, to what President Dwight Eisenhower termed the military industrial complex. And, in this schema, the DoD became the federal arm responsible for overseeing procurement of conventional and nuclear weapons.

Robert S. McNamara.

In the 1960 presidential race, President John F. Kennedy promised to eliminate the "missile gap" believed to have existed between the United States and The Soviet Union. Robert McNamara, named the Defense Secretary under John F. Kennedy, was responsible for the United States expansion of the country's arsenal of nuclear warheads as the DoD developed Intercontinental Ballistic Missiles (ICBMs) capable of delivering multiple warheads at targets in the Soviet Union and China.

Image of an U.S. military helicopter spraying Agent Orange in Vietnam.

Before being named Secretary of Defense, Robert McNamara was president at Ford Motor Company. When asked to join John F. Kennedy's cabinet, Robert McNamara immersed himself in defense issues and instituted key changes to U.S. Military doctrine. He also implemented programs in counterinsurgency to combat foreign Communist threats, including creating the Defense Intelligence Agency, expanding Army commando units, also known as Special Forces, for unconventional warfare, especially in the Vietnam War. McNamara also approved the strategic bombing campaigns against North Vietnam and the use of chemical defoliants such as Agent Orange.

Since McNamara, secretaries of defense have kept a lower profile. These have included Melvin Laird, who served under President Richard Nixon, and Donald Rumsfeld, who served under President Gerald Ford as the youngest Secretary of Defense and served a second term under President George W. Bush.

Clark Clifford served as the Secretary of Defense from 1968 to 1969 under Lyndon B. Johnson. Previous to his tenure as the Secretary of Defense, Clark Clifford served as a political adviser presidents Harry S. Truman, John F. Kennedy, Lyndon B. Johnson, and Jimmy Carter. During his time as secretary of defense, Clark Clifford followed the policies established by Robert McNamara on nuclear strategy, NATO, and military assistance, but did favor a Sentinel anti-ballistic missile system.

Melvin Laird, secretary of defense under President Richard Nixon.

Appointed by President Richard Nixon, Melvin Laird served as defense secretary from 1969 to 1973. During this time, Melvin Laird and President Nixon appointed a Blue Ribbon Defense Panel to make recommendations on the DoD's organization and functions, which were later implemented under Laird's leadership. He also departed from the management style of McNamara and Clifford, his predecessors in the role. This approach was to gain the cooperation of military leadership in reducing the defense budget and the size of the military establishment.

A lot of Melvin Laird's time in office was otherwise occupied with the Vietnam war. From the beginning of his time in office, Melvin Laird and Henry Kissinger (National Security Adviser to President Nixon) clashed over access to the president. Kissinger tried to remove Melvin Laird from the decision-making process over the Vietnam war, which included establishing a direct channel from Kissinger's office to the Joint Chiefs of Staff in an effort to isolate Laird. In 1969, President Nixon's strategy towards the war was to impose an armistice to preserve South Vietnam. Melvin Laird's overall impact in the office was to reduce the budget, which reduced the troops deployed in Vietnam and contributed to America's departure from Vietnam.

The F-14 Tomcat, developed during Donald Rumsfeld's first tenure as secretary of defense.

Under President Gerald Ford, Donald Rumsfeld's tenure was noted for pushing forward weapons programs intended to modernize America's nuclear and conventional arsenals. The 1970s saw research and development projects evolve into deployable systems, such as the Navy's F-14 Tomcat, the Air Force F-15 Eagle, and the Army's M1A Abrams Tank.

Casper Weinberger.

President Ronald Reagan named Caspar Weinberger his defense secretary. During this tenure, there was an increase in procurement programs in order to restore America's superiority on the world stage. This led to the most expensive arms buildup in United States history, even though Weinberger's reputation before taking office of defense secretary was as a budget trimmer. Both Reagan and Weinberger believed the Soviet Union posed a serious threat and the defense establishment needed to be modernized and strengthened to compete. The DoD budget increased to near $300 billion during the 1980s and saw the development of new aircraft carriers and controversial programs like the B-1 bomber and MX missile.

Rockwell B-1 Lancer

The efforts of Weinberger to develop and rebuild the United States' military and related forces strength were associated with the Perestroika and the beginning of the end of the Cold War and, following, the Soviet Union. The strategy of rearmament and building the U.S. military came from Weinberger's and Reagan's estimation that the Soviet Union was already showing stress as a result of the countries extreme focus on military production and an estimation that, if the United States developed its military further, the Soviet Union would be unable to sustain it's military production.

Despite the successes associated with Weinberger's procurement program, the program also had some setbacks. These included the Sergeant York air-defense gun that was supposed to give the Army greater protection from Soviet aircraft. The DoD spent $1.8 billion and ten years developing the tank-mounted, radar-guided gun, but field tests for the weapons had trouble hitting a hovering helicopter. The B-1 bomber was another experiment that did not work out as intended, as the plane was initially intended to be flown at low altitude to penetrate Soviet air defense, but the B-1 bomber was incapable of doing so. Originally developed to retire the aging B-52, designers realized the B-1 was vulnerable to air defenses and the B-52, rather than replaced, continues to serve in USAF squadrons.

Casper Weinberger was also part of the Iran-Contra affair of the Reagan era. The Iran-Contra affair involved the secret sale of U.S. weapons to Iran in exchange for the release of American hostages held in Lebanon by pro-Iranians terrorists, and the diversion of money from the sale to provide support for anti-communist resistance fighters in Nicaragua known as the "Contras". Weinberger was later charged by independent counsel Lawrence Walsh with four counts of lying to congressional Iran-Contra investigators in 1987 and for allegedly lying to Walsh's prosecutors in 1990. Weinberger pled not guilty and was pardoned by President George H.W. Bush in 1991 before the case went to trial.

With the end of the Cold War, DoD became less of a priority, and the operations of the Secretary of Defense placed less importance on defense spending and developing new weapons programs.

President George H. W. Bush nominated Cheney for the office of Secretary of Defense after the U.S. Senate failed to confirm John Tower for the position. Cheney served from March 1989 to January 1993. During his time as secretary of defense, Cheney directed the United States invasion of Panama and Operation Desert Storm in Iraq. In 1991, he was awarded the Presidential Medal of Freedom by President George H. W. Bush. He also received the U.S. Senator John Heinz Award for Greatest Public Service by an Elected or Appointed Guild Official, an award given out annually by Jefferson Awards.

During the two terms of President Bill Clinton, Les Aspin, William Perry and William Cohen served as defense secretaries. During the decade, the DoD's budget shrunk and the three secretaries of defense spent more time determining the shape and role the U.S. Military should take in a post-Cold War world. Programs designed to combat the Soviet military, such as the Seawolf attack submarine, were cut and doctrines emphasizing rapid deployment of conventional forces were developed to address smaller scale conflicts such as the growing threats from terrorist organizations.

Donald Rumsfeld

Donald Rumsfeld served a second tenure as defense secretary under President George W. Bush. Following the September 11, 2001 terrorist attacks, Rumsfeld became the face of the United States' new world posture to hunt down Osama bin Laden and other associated terrorist groups. Rumsfeld and his chief deputy, Paul Wolfowitz, were key architects of the president's global war on terrorism campaign, which included the invasions of Afghanistan and Iraq and planned attacks on Iran and North Korea. Rumsfeld also promoted increases in the DoD budget that eclipsed those of the Reagan era. Rumsfeld's second tenure brought controversy, especially with his championing of the president's approach to terrorist suspects and their supporters, and the Guantanamo Bay and Abu Ghraib scandals. There were also questions during Rumsfeld's tenure over the supply of United States troops and equipment during the Afghanistan and Iraq campaigns. President Bush asked Rumsfeld to resign following the 2006 election and the Republican loss of control of Congress. Robert Gates, former CIA director, replaced Rumsfeld.

Robert Gates

Following Donald Rumsfeld's resignation from the office of the defense secretary, Robert Gates was appointed as defense secretary. Gates immediately ordered an increase in the troop levels in Iraq, which had been resisted previously despite being called for by some military commanders and also went against the anti-war sentiment of Congress and voters at the time.

The 2008 election of President Barack Obama saw him withdraw U.S. combat troops from Iraq, which was completed in December 2011. However, following consideration and citing a "deteriorating situation" caused by surging al-Qaeda and Taliban forces, Obama eventually escalated the U.S. presence in Afghanistan by adding 30,000 troops to the 68,000 which had previously been stationed there. With scattered claims of successes amid instability and corruption in the Afghanistan government, and waning support for the war amongst the American public, President Obama announced a timeline for the United States and NATO troops to withdraw from Afghanistan by late 2014.

Leon Panetta

In 2011, former CIA director Leon Panetta took over as Secretary of Defense from a retiring Robert Gates. At the same time, the U.S. took a lead role in orchestrating and participating in, along with eighteen countries and fourteen NATO allies, a military operation to support and protect civilians in Libya from Colonel Muammar el-Qaddafi's attacks on the people of Libya. Also during his tenure, In May 2011, a number of United States military and intelligence agencies collaborated in the CIA-led assault on a compound in Abbottabad, Pakistan, where a team of U.S. Navy Seals killed terrorist leader Osama bin Laden.

As United States efforts against terrorist cells and leaders continue, the DoD began to increase the use of unmanned aerial vehicles (UAV), or drones. These systems locate and kill a target through the direction of a pilot and a team of up to 180 operators situated at a base many thousands of miles away. There has been a 1,200 percent increase in the use of drone patrols since 2005. There are more hours flown by drones than crewed aircrafts, and they have been used for tactical purposes in Afghanistan, Yemen, and Somalia. There is an expectation that drones will be further outfitted with artificial intelligence in order to give them the ability to make wartime decisions without an operator.

Early image of the Pentagon under construction.

The Pentagon is the headquarters for the Department of Defense. It is one of the world's largest office building with triple the amount of floor space of the Empire State Building in New York City. Construction of the Pentagon began on September 11, 1941 and it officially opened on January 14, 1943. The Pentagon was the brainchild of Army Brig. Gen. Brehon B. Sommervell, who, in the early 1940s, presented the idea as a temporary solution to the then-War Department's critical shortage of space as the threat of joining World War II loomed. It was believed the Pentagon was to be a short-term necessity during World War II. The plan was for the 296 acres of land to be turned into a hospital, office, or warehouse at the conclusion of World War II. But as the United States continued to expand its military presence throughout the world, the Pentagon remained the headquarters for the Department of Defense.

The Pentagon under construction.

The shape of the Pentagon was decided on by the five roadways that bordered the building, and the shape led to the building's name. The grounds and building were developed in sixteen months, and the building was officially completed in January 1943, thanks to the help of 1,000 architects and 14,000 tradesmen who worked three shifts around the clock. The materials used in the construction included 435,000 yards of concrete, 43,000 tons of steel, and 680,000 tons of sand and gravel. The first tenants moved into the building in April 1942, several months before the building was finished.

During the height of World War II, the Pentagon housed more than 33,000 people and its worth exceeded expectations as officials found that keeping a large military force active was easier with a centralized command structure and a building for that structure. The Pentagon remains as the military's command center. The building houses the Office of the Secretary of Defense, the Joint Chiefs of Staff, and the highest echelons of the Army, Navy, Marine Corps, and Air Force.

The Pentagon in the wake of the 9/11 attacks.

In 1992, the building was designated a National Historic Landmark. Due to its age, renovations began around this time on the 4 million square feet of space. In the September 11, 2001 attack on the Pentagon, it is believed that the renovations likely saved lives. The American Airlines Flight 77 crashed into the west side of the Pentagon and penetrated three of the building's five rings, killing 184 people. However, several offices in the area were not occupied because of the renovations and other upgrades that improved security features, including walls and windows that had been upgraded for greater blast resistance.

The reconstruction project of the Pentagon, dubbed the Phoenix Project, cost $500 million. The first tenants whose offices were damaged returned by August 15, 2002, despite the ongoing renovations. Part of the renovations included a new memorial to honor the lives of the 184 people killed at the Pentagon. The renovations began on June 15, 2006 and were completed and dedicated on September 11, 2008. The memorial sits on a two-acre plot of land on the southwest side of the building next to where the airplane struck.

The Pentagon under renovation.

The renovations before the 9/11 attacks on the Pentagon were already considered a large undertaking. The renovations included removing hazardous materials, replacing all building systems, adding new elevators and escalators to improve vertical circulation, installing new security and telecommunication systems, integrating sustainable design measures and force protection initiatives prompted by the 9/11 attacks, and environmental considerations. The last renovations included high-efficiency lights, recycled gypsum wall board, and recycled-content carpet. Ninety percent of all the concrete and metal was diverted from landfills.

According to Pentagon historians, 40,000 personnel had to be relocated during the project's various phases, which meant each wedge was broken into 10,000 square feet. The plumbers, electricians, and other tradesmen then had five days to complete their tasks before moving onto the next 10,000 square foot section.