Military branches:

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 (2008)

Military service age and obligation:

18 years of age; 17 years of age with written parental consent (2006)

Manpower available for military service:

males age 16-49: 72,715,332
females age 16-49: 71,638,785 (2008 est.)

Manpower fit for military service:

males age 16-49: 59,413,358
females age 16-49: 59,187,183 (2008 est.)

Manpower reaching militarily significant age annually:

males age 16-49: 2,186,440
females age 16-49: 2,079,688 (2008 est.)

Military expenditures - percent of GDP:

4.06% (2005 est.)