10 U.S.C. § 1208

(a) For the purposes of this chapter, a member of a regular component shall be credited with the service described in paragraph (1) or that described in paragraph (2), whichever is greater: (1) The service that he is considered to have for the purpose of separation, discharge, or retirement for length of service. (2) The sum of— (A) his active service as a member of the armed forces, a nurse, a reserve nurse, a contract surgeon, a contract dental surgeon, or an acting dental surgeon; (B) his active service as a member of the National Oceanic and Atmospheric Administration or the Public Health Service; and (C) his service while participating in exercises or performing duties under sections 502, 503, 504, and 505 of title 32. For the purpose of paragraph (2), active service as a member of the National Oceanic and Atmospheric Administration includes active service as a member of the Environmental Science Services Administration and of the Coast and Geodetic Survey. (b) A member of the armed forces who is not a member of a regular component shall be credited, for the purposes of this chapter, with the number of years of service that he would count if he were computing his years of service under section 12733 of this title .