During World War II, Diamond T produced a classic heavy truck in the 980/981, a prime mover which was 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. In addition Diamond T built the entire range of the G509 series 4 ton 6X6s, including cargo, dump, semi tractor, and wrecker trucks, as well as some lighter trucks, and even G7102 half tracks. Diamond T ranked 47th among United States corporations in the value of World War II military production contracts.
Diamond T manufactured two pickup trucks: the Model 80 and the Model 201. Both pickups were powered by the Hercules QX-series 6-cylinder engines. The Model 201 was produced from 1938 to 1949.