C. A. Tilt began building cars in 1905 and when one of his customers requested a truck he obliged. That was in 1911 and the truck was a 1 1/2-tonner with chain drive. Tilt's emblem of the Diamond T Motor Car Co. was his initial "T" set within a diamond which symbolized quality. The company built only trucks from 1911 onwards and as early as 1915 had built up a national reputation for its products which ranged from 2 to 5-ton payload. Diamond T Model B Liberty trucks were built in large numbers during World War I and development took place throughout the 1920s and '30s. In 1928 the trucks boasted 6-cylinder engines, spiral-bevel rear axles and all-wheel braking. By then heavier six-wheeled trucks were being offered for 12-ton payloads. In the mid '30s the trucks were given stylish new cabs and by 1937 the first cabover models were appearing. During World War II Diamond T built their legendary 6x6 trucks and 6x4 12-ton tank tractors which were widely used as heavy-haulage tractors after the war.
A new range was launched in 1947 and bv 1951 lighter trucks had been dropped. From then on production was concentrated on heavy-duty trucks, both normal and forward-control. Also in 1951 a new design of forward-control tilt cab appeared. This was also used on certain Hendrickson and International trucks. Diamond T was taken over by the White Motor Co . in 1958 and the word "Car" in the company title was changed to "Truck". In 1961 production was transferred to the company's Reo factory, also in White ownership from 1957. From 1967 Diamond T and Reo products were merged and the trucks were renamed Diamond Reo, a sub-division of the White Motor Corp .
A range of heavy-duty conventionals and cabovers were built under the new name up until 1971 when White sold the division to Francis L. Coppaert of Birmingham, Alabama. Under new ownership and independent once again, Diamond Reo Trucks Inc., as it was now called, developed some successful new models. These were the Royale with a choice of straight six, engines, and the Apollo conventionals with a choice of Caterpillar. Cummins or Detroit Diesel power units. Their bonneted, heavy 6x4 tractor, the Raider, appeared in 1974. While sales were healthy in the early 1970s, Diamond Reo fell into financial problems in 1975 and the receivers were called in. The company was then of the Diamond Reo parts distributors, Osterlund Inc. of Hansbury, Pennsylvania. From that point on one basic model, the bonneted Giant, was available in 4x2, 4x4, 6x4 and 6x6 form mainly for the construction industry.