Prior to the publication of the June 1945, Manual of Military Occupational Specialties NAVMC 1008-PD, the Marine Corps generally followed the Army's system for classifying jobs for personnel. As stated in the manual, the Marine Corps often used Army publications  for determining military SSN's . After the publication of this manual, it would be the sole reference for classifying military personnel in the Marine Corps. The Army Manual, TM-12 426 would still be used for civilian personnel.
List of Vietnam War Era USMC Military Occupational Specialty Codes (MOS Codes), verified from information included in the Defense Casualty Analysis Extract File (DCAS), at the National Archives.