Model 980/981 12-ton 6x4 trucks (G159) were ballast tractors used as tank transporters. Designed for the British military they were also used by the US Army. Powered by a Hercules DFXE diesel engine developing and geared very low, it could pull a trailer of up to and proved capable of the task of moving the heaviest tanks then in service. Early trucks used a standard Diamond T commercial cab (also used by the 4-ton G509 trucks). In August 1943 it was replaced with an open military cab. A long butterfly hood had vertical louvers along both sides.