The 0331 Machine Gunner is the primary MOS for enlisted infantry Marines who operate man portable medium and heavy machineguns as part of the Infantry Battalions' weapons platoons and companies.
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The Machine Gunner is responsible for the tactical employment of the 7.62 mm Medium Machine-Gun, the 50 cal., and 40mm Heavy Machine-Gun, and their support vehicle. Machine Gunners provide direct fire in support of the Infantry Rifle squads/platoons/companies. They are located in the weapons platoons of the rifle and weapons company in the infantry battalion. Noncommissioned Officers are assigned as team leaders and squad leaders/section leaders.