United States Departmnet of Defence

The Department of Defense (DOD) is an executive branch department of the federal government of the United States charged with coordinating and supervising all agencies and functions of the government concerned directly with national security and the United States Armed Forces. The Department is also the largest employer in the world, with more than 2.13 million active duty servicemen and women as well as their support staff of civilian workers. Adding to the total is over 1.1 million National Guardsmen and Reservists from the four services, bringing the total to just over 3.2 million employees.

The Department of Defense is headed by the Secretary of Defense, a cabinet-level head who reports directly to the President of the United States. Beneath the Department of Defense are three subordinate military departments: the United States Department of the Army, the United States Department of the Navy, and the United States Department of the Air Force. In addition, four national intelligence services are subordinate to the Department of Defense: 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 including the Defense Advanced Research Projects Agency (DARPA), the Defense Logistics Agency (DLA), the Missile Defense Agency (MDA), Defense Threat Reduction Agency (DTRA), and the Pentagon Force Protection Agency (PFPA), all of which are under the command of the Secretary of Defense. Military operations are managed by nine regional or functional Unified Combatant Commands. The Department of Defense also operates several joint services schools, including the National Defense University (NDU) and the National War College (NWC).

The Secretary of Defense, appointed by the President with the advice and consent of the Senate. He is by the head of the Department of Defense, "the principal assistant to the President in all matters relating to Department of Defense", and has "authority, direction and control over the Department of Defense" Because the Constitution vests all military authority in Congress and the President, the statutory authority of the Secretary of Defense is derived from their constitutional authorities. Since it is impractical for either Congress or the President to participate in every piece of Department of Defense affairs, the Secretary of Defense, and the Secretary's subordinate officials generally exercise military authority.

The Department of Defense is composed of the Office of the Secretary of Defense (OSD), the Joint Chiefs of Staff (JCS) and the Joint Staff (JS), Office of the Inspector General (DODIG), the Combatant Commands, the Military Departments (Department of the Army (DA), Department of the Navy (DON) & Department of the Air Force (DAF)), the Defense Agencies and Department of Defense Field Activities, the National Guard Bureau (NGB), and such other offices, agencies, activities, organizations, and commands established or designated by law, or by the President or by the Secretary of Defense.

The United States Air Force (USAF) is the aerial warfare service branch of the United States Armed Forces and one of the seven American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on 18th September of 1947 under the National Security Act of 1947. It is the most recent branch of the U.S. military to be formed, and is the largest and one of the world's most technologically advanced air forces. The USAF articulates its core functions as Nuclear Deterrence Operations, Special Operations, Air Superiority, Global Integrated ISR, Space Superiority, Command and Control, Cyberspace Superiority, Personnel Recovery, Global Precision Attack, Building Partnerships, Rapid Global Mobility and Agile Combat Support. The U.S. Air Force is a military service within the Department of the Air Force, one of the three military departments of the Department of Defense. The USAF is headed by the civilian Secretary of the Air Force, who is appointed by the President with the advice and consent of the Senate. The highest-ranking military officer in the Department of the Air Force is the Chief of Staff of the Air Force who exercises supervision over Air Force units, and serves as a member of the Joint Chiefs of Staff. Air Force combat forces and mobility forces are assigned, as directed by the Secretary of Defense, to the Combatant Commanders, and neither the Secretary of the Air Force nor the Chief of Staff have operational command authority over them.

The U.S. Air Force provides air support for surface forces and aids in the recovery of troops in the field. As of 2012, the service operates more than 5,638 military aircraft, 450 ICBMs and 63 military satellites. It has a $140 billion budget with 309,339 active duty personnel, 185,522 civilian personnel, 71,400 Air Force Reserve personnel, and 106,700 Air National Guard personnel.

The United States Army is the largest branch of the Armed Forces of the United States that performs land-based military operations; and is one of the seven Uniformed services of the United States. As the largest and senior branch of the U.S. military, the modern U.S. Army has its roots in the Continental Army, which was formed (14 June 1775) to fight the American Revolutionary War (1775–83)—before the U.S. was established as a country. After the Revolutionary War, the Congress of the Confederation created the United States Army on 3 June 1784, to replace the disbanded Continental Army. The United States Army considers itself descended from the Continental Army, and dates its institutional inception from the origin of that armed force in 1775.

As a uniformed military service, the Army is part of the Department of the Army, which is one of the three military departments of the Department of Defense. The U.S. Army is headed by a civilian officer, the Secretary of the Army, and by a chief military officer, the Chief of Staff of the Army. The ranking officer of the U.S. Army is the Chairman of the Joint Chiefs of Staff. In the fiscal year 2011, the Regular Army (USA) reported a strength of 546,057 soldiers; the Army National Guard (ARNG) reported 358,078 soldiers, and the United States Army Reserve (USAR) reported 201,166 soldiers; the combined-component strength of the U.S. Army was 1,105,301 soldiers. As a branch of the armed forces, the mission of the U.S. Army is "to fight and win our Nation's wars, by providing prompt, sustained, land dominance, across the full range of military operations and the spectrum of conflict, in support of combatant commanders."

The United States Army serves as the land-based branch of the U.S. Armed Forces. The §3062 of Title 10 US Code defines the purpose of the army as:

• Preserving the peace and security and providing for the defense of the United States, the Commonwealths and possessions and any areas occupied by the United States

• Supporting the national policies

• Implementing the national objectives

• Overcoming any nations responsible for aggressive acts that imperil the peace and security of the United States

The United States Navy (USN) is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest, most powerful navy in the world, with the highest combined battle fleet tonnage. The U.S. Navy has the world's largest aircraft carrier fleet, with ten nuclear carriers in service, with two under construction. The service has 325,143 personnel on active duty and 107,355 in the Navy Reserve. It has 272 deployable ships and more than 3,700 aircraft in service as of March 2015.

The U.S. Navy traces its origins to the Continental Navy, which was established during the American Revolutionary War and was essentially disbanded as a separate entity shortly thereafter. It played a major role in the American Civil War by blockading the Confederacy and seizing control of its rivers. It played the central role in the World War II defeat of Japan. The 21st century U.S. Navy maintains a sizable global presence, deploying in such areas as East Asia, the Mediterranean, and the Middle East. It is a blue-water navy with the ability to project force onto the littoral regions of the world, engage in forward areas during peacetime, and rapidly respond to regional crises, making it an active player in U.S. foreign and defense policy.

The Navy is administratively managed by the Department of the Navy, which is headed by the civilian Secretary of the Navy. The Department of the Navy is itself a division of the Department of Defense, which is headed by the Secretary of Defense. The Chief of Naval Operations (CNO) is a four-star admiral and the senior naval officer of the Department of the Navy. However, the CNO may not be the highest ranking naval officer in the armed forces if the Chairman or the Vice Chairman of the Joint Chiefs of Staff are Navy officers, who by law, outrank the CNO.

The United States Marine Corps (USMC) is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the U.S. Navy to rapidly deliver combined-arms task forces. The U.S. Marine Corps is one of the four branches in the U.S. Department of Defense as a member of the Joint Chiefs of Staff. It is one of the seven uniformed services of the United States.

The Marine Corps has been a component of the U.S. Department of the Navy since 1834, working closely with naval forces for training, transportation, and logistics. The USMC operates posts on land and aboard sea-going amphibious warfare ships around the world, and several of the Marines' tactical aviation squadrons, primarily Marine Fighter Attack squadrons, are also embedded in Navy carrier air wings and operate from the Navy's nuclear-powered aircraft carriers.

The United States Coast Guard (USCG) is a branch of the United States Armed Forces and one of the country's seven uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the U.S. military branches for having a maritime law enforcement mission (with jurisdiction in both domestic and international waters) and a federal regulatory agency mission as part of its mission set. It operates under the U.S. Department of Homeland Security during peacetime, and can be transferred to the U.S. Department of the Navy by the U.S. President at any time, or by the U.S. Congress during times of war. To date, this has happened twice, in 1917 and 1941, during World War I and World War II, respectively.

Created by Congress on 4 August 1790 at the request of Alexander Hamilton as the "Revenue Marine", it is the oldest continuous seagoing service of the United States. As Secretary of the Treasury, Hamilton headed the Revenue Marine, whose original purpose was that of a collector of customs duties in the nation's seaports. By the 1860s the service was known as the U.S. Revenue Cutter Service and the term Revenue Marine gradually fell into disuse.