 Complete the following phrase:  The M13 Multiple Gun Motor Carriage MGMC, otherwise known as the M13 half-track, was a self-propelled anti-aircraft gun used by the U.S. Army during World War II that was armed with two .50 caliber M2HB heavy-barrel Browning machine guns. Developed in response to a requirement for a mobile anti-aircraft AA vehicle, the vehicle was produced by the White Motor Company between July 1942 and May 1943. The only time it was ever used in combat was when the Americans 