As a general rule, military service in the Armed Forces of the United States is creditable for retirement purposes if it was active service terminated under honorable conditions, and performed prior to your separation from civilian service for retirement.
Military deposits include interest unless they are paid within a grace period. Payments must be made to your employing agency before you separate. They cannot be paid to the U.S. Office of Personnel Management.
Additional information regarding military deposits is on the service credit page.