The M39 series 5-ton 6×6 truck (G744) was a family of heavy tactical trucks built for the United States Armed Forces. The basic cargo version was designed to transport a 5-ton (4,500 kg), 14 ft (4.3 m) long load over all terrain in all weather. In on-road service the load weight was doubled. The M39 series was the primary heavy truck of the U.S. Army and U.S. Marine forces during the Vietnam War, and was also used by the U.S. Navy, U.S. Air Force, and ARVN forces.