From the Document: "The Department of Defense (DOD) workforce consists of military personnel, civilian employees, and contractors. A DOD civilian does not serve in the military but is instead appointed to the federal civil service. DOD civilians work for the military departments (i.e., Army, Navy, and Air Force) as well as other defense agencies and field activities (e.g., Defense Health Agency). Federal civilians have supported the armed forces as far back as the American Revolution. For example, in World War II, civilians provided medical and logistics support to military personnel. The DOD civilian workforce has evolved over time to meet the growing needs of the department and the changing landscape of national defense."
CRS In Focus, IF11131
Congressional Research Service: https://crsreports.congress.gov/