The Department of Defense is America's oldest and largest government agency. With our military tracing its roots back to pre-Revolutionary times, the Department of Defense has grown and evolved with our nation. Today, the Department, headed by Secretary of Defense Robert Gates, is not only in charge of the military, but it also employs a civilian force of thousands. With over 1.3 million men and women on active duty, and 684,000 civilian personnel, we are the nation's largest employer. Another 1.1 million serve in the National Guard and Reserve forces. More than 2 million military retirees and their family members receive benefits.