U.S. Department of Defense

The United States Department of Defense is responsible for providing the military forces needed to deter war and protect U.S. security. The major elements of these forces are the Army, Navy, Marine Corps, and Air Force, consisting of about 1.4 million men and women on active duty.  Of these, roughly half a million serve outside U.S. borders. In an emergency, these forces are supplemented by the 900,000 reserve component. There are also about 800,000 civilian employees in the Defense Department.  Under the President, who is also Commander in Chief, the Secretary of Defense exercises direction, authority and control over this Department.