D-4 Caterpillar Bulldozer

The diesel powered Caterpillar D4 evolved from the Cat R4 gasoline tractor. In 1936, the Cat R4 was joined by the diesel RD4 (4G series) and in 1937 the RD4, with some minor modifications, was renamed the D4 (4G series).

The early D4 models (4G, 7J, 2T, 5T) were powered by the Cat D4400 engine developing 35 drawbar horsepower. A small gasoline pony motor was used to start the diesel. The 6U and 7U were upgraded to the Cat D315 4 cyl diesel with 43 drawbar hp.

Caterpillar D4 tractor mired in deep mud during Alcan Highway construction, Alaska, 1942
Caterpillar D4 tractor mired in deep mud during Alcan Highway construction, Alaska, 1942.

Today in WW II: 4 Jul 1942 German bombers and submarines sink 24 ships of Convoy PQ 17 to the Soviet Union after the convoy spread out in the Arctic Ocean to evade the German battleship Tirpitz.  More ↓
4 Jul 1942 US Eighth Air Force flies its first mission in Europe using six borrowed British planes; only three aircraft returned.
Visit the Olive-Drab.com World War II Timeline for day-by-day events 1939-1945! See also WW2 Books.

D-4 Caterpillar Bulldozer

During WW II, the D4 was one of the tractor/bulldozers collectively known as "Tractor, Light." The Caterpillar D4 models were Ordnance G-151. Equivalent tractors were produced during WW II by International Harvester Co. (Model TD9, G-99). The Cat D4 was used as a prime mover for light artillery, for general duty as a tractor, or as a bulldozer when equipped with a suitable blade attachment.

The evolution of the D4 included these models:

  • D4 4G series 1937-1938, Orchard model
  • D4 7J series 1939-1942
  • D4 2T series 1943-1945
  • D4 5T series 1945-1947
  • D4 6U series 1947-1959, 44 inch gauge
  • D4 7U series 1947-1959, 60 inch gauge

Over 7,400 of the 5T series were built and over 44,000 7U units were produced. Tractor serial numbers were composed of the series (eg 4G, 6J) followed by a four or five digit serial number. With modifications and additional series, the D4 continued in production and remains in the Caterpillar product line in the mid-2000s.

Thanks to Stephen A. Sarkany for help with this page.

Caterpillar D4 tractor in use during Alcan Highway construction, 1942
Caterpillar D4 tractor in use during Alcan Highway construction, 1942.

Caterpillar D4 tractor in use on Attu Island, Aleutians, May 1943
Caterpillar D4 tractor in use on Attu Island, Aleutians, May 1943.

Caterpillar D4 tractor configured as a bulldozer belonging to U.S. Fifth Army, on raft in Volturno River, Italy, October 1943
Caterpillar D4 tractor configured as a bulldozer belonging to U.S. Fifth Army, on raft in Volturno River, Italy, October 1943.