This site gives a pretty good breakdown of the US and other countries (although not by branch):
Military branches:
Department of the Army, Department of the Navy (includes Marine Corps), Department of the Air Force
note: the Coast Guard is normally subordinate to the Department of Transportation, but in wartime reports to the Department of the Navy
Military manpower - military age:
18 years of age (2002 est.)
Military manpower - availability:
males age 15-49: 73,597,731 (2002 est.)
Military manpower - fit for military service:
NA
Military manpower - reaching military age annually:
males: 2,093,263 (2002 est.)
Military expenditures - dollar figure:
$276.7 billion (FY99 est.)
Military expenditures - percent of GDP:
3.2% (FY99 est.)
Military - note:
note: 2002 estimates for military manpower are based on projections that do not take into consideration the results of the 2000 census
Total DoD Army Navy Marines AirForce Coast Guard
Total Active Duty Military
(as of April 30, 2002) 1,398,238 481,266 381,901 172,741 362,330 36,914
Civilian Employees
(as of April 2002) 667,715 230,130 183,473 151,664 5,715 102,448
This is active duty only Reserves and National Guard add roughly 1.5 Million more to these totals.