By 1967, as a subsidiary of White Motor Company, it was merged with Reo Motor Company to become Diamond Reo Trucks, Inc.[2] During World War II, Diamond T produced a prototype of a heavy truck in the 980/981, a prime mover which was adapted and quickly acquired by the British Purchasing Commission for duty as a tank transporter tractor.

Coupled with a Rogers trailer, the truck gave sterling service with the British Army in North Africa Campaign, where its power and rugged construction allowed the rescue of damaged tanks in the most demanding of conditions.

[3] [citation needed] In addition Diamond T built the entire range of the G509 series 4 ton 6X6s, including cargo, dump, semi tractor, and wrecker trucks,[4] as well as some lighter trucks, and even G7102 half tracks.

[5] Diamond T ranked 47th among United States corporations in the value of World War II military production contracts.

By 1929 there were chassis load ratings (the weight of the body and payload) up to 12 tons (10,900 kg) on three axles.

In a 1935 model year style change it had been improved with a "streamlined" V-style windshield.

Powered by a 895 cubic inches (14.7 L) Hercules DFXE diesel engine developing 185 horsepower (138 kW) and geared very low, it could pull a trailer of up to 115,000 pounds (52,000 kg) and proved capable of the task of moving the heaviest tanks then in service.

There were closed tool compartments along both sides, two open containers in the front, and a bottom-hinged tailgate.

The box could hold 18,000 pounds (8,200 kg) of ballast to increase traction on the rear tandem axles.

[4][9] Standard models were powered by the 6 cyl., 529 cubic inches (8.7 L) Hercules RXC engine that developed 106 horsepower (79 kW) mated to a five speed manual transmission and two speed transfer case.

[4][9] Model 967 was a pre-standard prime mover cargo truck (21 were built as wreckers).

Produced in early 1941, it was fitted with Hercules RXB 501 cubic inches (8.2 L) inline six cylinder engine.

[4] Model 972 dump truck was the largest the US Army had during World War II.