Michigan Compiled Laws, Chapter 32. Military Establishment § 32.817

(a) Active service in the Michigan national guard or Michigan defense force as an officer or enlisted man or both.

(b) Federal service in response to a call or order of the president in time of declared national emergency when such service is not voluntary.

(c) Voluntary active duty in the service of the United States by members of the state military establishment, not in response to a call or order of the president in time of declared national emergency, shall be considered as active service only when such duty is in support of a national guard mission. Any fractional part of a year amounting to 6 months or more is counted as a complete year. Active service is terminated by an honorable separation from the Michigan national guard or defense force.