Of a total of 686,000 personnel on active duty, 560,000 were in the army, 63,000 in the navy and marines, and 63,000 in the air force. An additional 4.5 million were in the reserves. Paramilitary forces included 3.5 million in the Civilian Defense Corps. Equipment included over 2,000 main battle tanks, 20 submarines, and 538 combat aircraft. South Korea provided support for peacekeeping and UN missions in six regions. The US maintained a military presence of 37,140 personnel. Defense spending was $12.8 billion in 2001 or 2.8% of GDP.