Department of Defence; Military Department= Department of Defense = Prior to the Korean War the Department of Defense (DoD) was known as the War Department. (Editor's Note: I am uncertain of the exact date when this was changed, but it was after World War II).
- the Air Force
- the Navy
- the Marine Corps
- the Army
- the Coast Guard
The United States military is currently (2003) an all volunteer organization whos members volunteer for a term of anywhere from 2 - 6 years.
Each branch of the US military has a reserve branch as well, known colloquially as "weekend warriors" because the active reserve units meet one weekend a month to train. In addition to the weekend obligation members of the active reserves also serve two weeks of the year on active duty, i.e. in a currently functioning military unit.