The Caterpillar Diesel Forty is an agricultural crawler tractor produced from 1934 to 1936 by Caterpillar in Peoria, Illinois, USA. It features a Caterpillar D6600 3-cylinder liquid-cooled diesel engine with 10.2 L displacement, a 4-speed gear transmission with 1 reverse, and a crawler drive. The tractor has an open operator station and weighs 15642 lbs (7095 kg) with 16-inch tracks. It delivers 50.44 hp drawbar power and 56.05 hp belt power. Serial numbers range from 3G1 in 1934 to 3G1971 as the final number in 1936.