The military website Olive-Drab describes the Caterpillar D4 as a versatile industrial machine that could double as a tractor or a bulldozer. A diesel engine primed by a gas-powered motor gave the vehicle a hauling strength of 35 horsepower, later upgraded to 43 horsepower. According to VanNatta Forestry & Logging, the D4's solid design and cast-iron construction made it extremely durable.
The D4 developed from an earlier gasoline-powered Caterpillar vehicle, the R4. The D4 continued to evolve from 1937's G4 Series through the 7U Series of the 1940s and 1950s. Caterpillar continued to build new D4s well into the 2000s.
The D4 saw widespread action during World War II under the U.S. Army moniker of Ordnance G-151. It could perform as a bulldozer with its bulldozer blade in place, but it also transported light artillery and served as a tractor. VanNatta Forestry & Logging notes that it also proved its worth in the logging industry.
The Caterpillar D4 bulldozer has served as a workhouse for industrial and military applications since the late 1930s. These diesel-powered vehicles proved slow but sturdy, as well as remarkably versatile.