Nevertheless, the QMC and Willys kept developing the ton 6x6, in various versions, as the "Super-Jeep". By March 1942, the T14 GMC was revised as a cargo / prime mover, named Willys 'MT-TUG', that could compete in some roles with the ton Dodges. The Army tested these in various configurations, up to a 1-ton rated version, as a light, multi-purpose tractor truck, cargo, or personnel carrier. For the Army Air Force / (US)AAF, several MT-Tug units were built with a fifth-wheel coupling on the cargo floor, for various Fruehauf trailers, and loaded with sandbags on the cargo bed, even as aircraft tugs. The Marine Corps also wanted a beefier truck, using standard jeep components, with higher fixed side body structure, as a personnel or mortar squad carrier, or an 'MT-CA' field ambulance.