Military branches:
United States Armed Forces: US Army, US Navy (includes Marine Corps), US Air Force, US Coast Guard; note - Coast Guard administered in peacetime by the Department of Homeland Security, but in wartime reports to the Department of the Navy (2009)
Military service age and obligation:
18 years of age (17 years of age with parental consent) for male and female voluntary service; maximum enlistment age 42 (Army), 27 (Air Force), 34 (Navy), 28 (Marines); service obligation 8 years, including 2-5 years active duty (Army), 2 years active (Navy), 4 years active (Air Force, Marines) (2010)
Manpower available for military service:
males age 16-49: 73,270,043
females age 16-49: 71,941,969 (2010 est.)
Manpower fit for military service:
males age 16-49: 60,620,143
females age 16-49: 59,401,941 (2010 est.)
Manpower reaching militarily significant age annually:
male: 2,161,727
female: 2,055,685 (2010 est.)
Military expenditures:
4.06% of GDP (2005 est.)
country comparison to the world: 24
(Source: website of U.S. Central Intelligence Agency)