ontains options for the M13 (twin .50cal) & the M16 (quad .50cal). The M13 MGMC was the product of the US army?s long-standing requirement for an anti-aircraft vehicle to protect its mechanized forces. The M13 consisted of twin .50 cal machine-guns mounted on an electrically operated turret developed by the Maxson Co., on a modified M3 half-track personnel carrier. Standardised in September 1942, it was re-designated Substitute Standard upon standardisation of the M16 MGMC (multiple gun motor carriage) quad .50 cal.