In 1939–1941 the Army Ordnance Corps was developing a complete line of tactical trucks that could operate over all roads and cross-country terrain in all weather.

In 1941 their improved Model 50SD6, with a larger engine and different hood and fenders, was standardized and went into production, but White Motor Company soon became their largest producer.

A Timken transfer case had a high and low range, a neutral for Power take-off (PTO) operation, and engaged the front axle.

[9] Prime movers and tankers had 10.00×22 size tires, while bridge, crane, and semi-tractor trucks had 14.00×20s with a larger cross-section.

[11] Prime movers were used to tow field artillery pieces, they also transported gun crews, equipment, and ammunition.

A mid-mounted 25,000 lb (11,000 kg) winch had a centered cable drum and a capstan on the right side.

Pulleys and rollers routed the cable under the body and out the rear frame cross-member.

[3][12] Built on a long, reinforced chassis, they were used to carry treadway pontoon bridges for Engineer Combat Battalions.

[13] A large double arm hydraulic boom built by Heil was used to self unload components, often directly into a river.

They had an auxiliary air compressor and large reservoir tanks, used to inflate pontoon floats.

The rotating crane was powered by an auxiliary IHC 334 cu in (5.5 L) inline 4 cylinder engine developing 35 hp (26 kW).

[6][17] As artillery pieces were being towed more often by tracked vehicles, prime mover chassis became available for other uses.

Mack used a Continental R-6602 developing 225 hp (168 kW) to drive a Hale centrifugal pump capable of 325 US gal/min (1,230 L/min) at 500 psi (3,400,000 Pa).

[20][21] White built communication vans for the Army Air Force on the prime mover wheelbase.