MOS Numbers

Every Marine is first and foremost a rifleman – but after that, they come in all varieties.

There are hundreds of specialized jobs in the Marine Corps, ranging from machine gunner to upholsterer. An individual’s specialty might be defined by his pre-war experience (a waiter becoming a cook), his abilities in boot camp (a natural leader becoming a DI), his performance on aptitude tests (a mechanical wiz becoming an aviation crew chief), where his name fell in the alphabet (for the sake of expediency) or – very rarely – his personal preference. There were even administrators who were classified as experts in the classification of others. Of course, the needs of the Corps were paramount, which led to a great deal of dissatisfaction among recruits, though most either adapted to their new jobs or managed to switch once assigned to their permanent unit.

A three-digit system was employed to quickly identify an individual’s area of expertise. (A similar, four-digit system is in use today.) Beginning in 1944, these numbers were printed in the muster rolls of virtually every Marine Corps unit.

This excerpt from the April 1944 muster roll of 1/24 shows the MOS system in place.
This excerpt from the April 1944 muster roll of 1/24 shows the MOS system in place.

By looking at the MOS numbers, researchers can better determine what part an individual played in a battle. In the example above, there are several riflemen (745) and a BAR gunner (746). Though all on this list were PFCs at the time, Raymond Cable and Harold Carter had the extra responsibility of leading a fire team (653). It can be presumed that Otto Cesco and Joey Chalifour were acquainted – not only were they in the same company, but both were machine gunners (604) and hence in the same platoon.

Unfortunately, MOS interpretation is not always exact. Battle casualties might elevate an MOS 745 to the position of squad leader (737), but his primary qualification remains a rifleman. The assignation of 521 – “Basic” – could mean any number of jobs; a “Basic” Marine was one who either lacked a specialty or was in the process of switching positions. However, as a basic guideline, it serves its purpose.

In the biography pages, readers will note the use of numerous MOS codes. The most common of these appear below, but for a much more complete list please visit The Military Yearbook Project.

050 Carpenter
055 Clerk
060 Cook
345 Truck Driver, Light or Chauffeur
405 Clerk, Typist
505 Ammunition Technician
521 Basic
522 Guard
533 Demolitions Specialist
585 First Sergeant
600 Machine Gun Squad Leader
604 Machine Gun Crewman
607 Mortar Crewman
614 Mortar Squad Leader
636 Intelligence Man
641 Telephone Man
651 Section Leader
653 Fire Team / Squad Leader (through end of 1944)
737 Fire Team / Rifle Squad Leader (1945)
745 Rifleman
746 Automatic Rifleman
776 Radio Operator
781 Flamethrower
812 Infantry Chief
0200 Communications Officer
1542 Infantry Officer
1930 Liaison

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