The British armed forces, sometimes called the services , consist of the Army , the Royal Navy ( RN ), and the Royal Air Force ( RAF ). The Queen is Commander-in-Chief of all three services, but responsibility for their management lies with the Ministry of Defence ( MOD ), which is headed by the Secretary of State for Defence . The Army is the largest of the three services and the Royal Navy the smallest. The Navy is the service with the longest history and is sometimes known as the senior service . The regular forces are supported when necessary by the regular reserves , who are former members of the regular forces and volunteer reserves , people who train in their free time with the Territorial Army , the Reserve Air Forces , or the Royal Navy Reserve . In 1998 the government’s Strategic Defence Review set out a plan of modernization of the armed forces and established a Joint Rapid Reaction Force which includes all three services.
In the US the President is Commander-in Chief of the armed forces and the Secretary of Defense is responsible for their management. The Joint Chiefs of Staff are the military leaders of the four services, the Army , Navy , Air Force and Marine Corps , which are supported when necessary by the reserve forces, the US Army Reserve , the National Guard and the Navy Reserve . The Army is the service with the longest history. Four of its leaders became President: George Washington, Andrew Jackson, Ulysses S Grant and Dwight Eisenhower.