"The military retirement system applies to members of the Army, Navy, Marine Corps, and Air Force. However, most of the provisions also apply to retirement systems for members of the Coast Guard (administered by the Department of Homeland Security), officers of the Public Health Service (administered by the Department of Health and Human Services), and officers of the National Oceanic and Atmospheric Administration (administered by the Department of Commerce). Only those members in plans administered by the Department of Defense (DoD) are included in this report, except in cases where Coast Guard data is shown for informational purposes. The system is a funded, noncontributory defined benefit plan that includes non-disability retired pay, disability retired pay, retired pay for reserve service, survivor annuity programs, and special compensation programs for certain disabled retirees. The Service Secretaries may approve immediate non-disability retired pay at any age with credit of at least 20 years of active duty service. Reserve retirees generally must be at least 60 years old and have at least 20 qualified years of service before retired pay commences; in some cases the age can be less than 60 if the reservist performed certain types of active duty service. There is no vesting of defined benefit entitlements before retirement; however, other military retirement system benefits may have lower vesting requirements."
Department of Defense, Office of the Actuary: http://www.actuary.defense.gov/