DMDC collects and reports on personnel, manpower, and other data for the DOD. Some of their statistics and reports are available to the public, others require a login. The library can not obtain access for you, however, points of contact for access are listed on the site.
1997 forward. Recent and historical personnel trends in the Department of Defense services and the U.S. Coast Guard. It describes demographic characteristics of applicants, accessions, enlisted personnel, and officers and includes information on the socioeconomic characteristics of those accessed into the military.