The standard and the long used by the pontoon cargo truck. (Measurements are from the centerline of the front axle to the centerline of the rear tandem). Tires were 9.00x20 with dual rear tires. Brakes were full air with drum brakes on all wheels. Trailer air connections applied trailer-brakes with the truck brakes and a hand lever could apply the trailer brakes alone. Early models had commercial type cabs, in June 1944 open military type cabs were introduced. These were easier to use in combat and also reduced shipping height, very important at the time. Both cab types could be equipped with a ring for a .50 cal. machine gun and every fourth truck was equipped with one. The basic cargo model was a prime mover used to tow the 155 mm howitzer M1 and transport the gun crew, equipment, and ammunition. They had a pintle hitch at the rear to tow up to off-road and on road. With a short wheelbase and rear overhang, the body could only be feet long. It had sideboards with fold down troop seats and bows for an overhead tarpaulin. Two spare tires were mounted inside the body, across the front. Early models had all steel bodies, in 1942 they were replaced by largely wood types to conserve steel. The wrecker had a Holmes twin-boom design with a swinging boom and powered hoist cable on each side. When towing the booms were rotated to the rear, connected at the ends, and worked as one A-frame. When lifting the booms could be separated and rotated 90% forward to the side, an outrigger could be lowered to increase lifting capacity. A power take-off on the transfer case drove a transmission with two winches in the wrecker frame. Controls on both sides of the body allowed each winch to raise or lower independently of the other. The body had low sides on the rear half which tapered to the floor in the front, making clearance for the boom to swing. A brace for the wrecker frame held a spare tire. Welding tanks, an air compressor, cables, block and tackle, chains, tow-bars, and other equipment were carried. The prime mover had limited cargo room, the Engineers wanted a model with a larger body to carry bridge pontoons. The spare tire was moved behind the cab and a ` long bed was placed further back on the chassis. The wheelbase was increased as the rear tandem was moved back for weight distribution.