Caterpillar was formed in 1925 by the merger of C.L. Best Tractor Company and the Holt Tractor Co. The D7 then known as the RD7 9G, was produced from 1935-1940. In 1937 Cat dropped the R designation from the name. These had a four cylinder diesel engine producing approx. 69 draw bar h.p. and 82 belt h.p. The D8800 engine was started by a “pony engine” that had a hand crank called a “grip” by Caterpillar. This was a gas powered engine that had two cylinders. Earlier D7’s had the crank protruding thru the left lower side skirt below the pony engine and later versions had it sticking up through the left front of the hood. The operator could start the engine from standing on the tracks. Two main levers steered the tractor via clutches in the rear drive. Other controls such as gear selector, throttle, and blade controls were at the driver’s disposal. These vehicles, whether it was Caterpillar, Allis Chalmers, IH, or Cleveland tractor, were all originally just tractors. They were purchased as prime movers. Until the advent of the accessories like blades, winches, cranes, and other mounted items, they were mostly used as tugs. The first armored bulldozer was developed by the British during World War II. This was a conventional Caterpillar bulldozer fitted with armor to protect the driver and the engine. The work was carried out by Jack Olding & Company Ltd. of Hatfield. The bulldozer was one of several strange armored vehicles that were collectively referred to as "Hobart's Funnies" and were operated by the British 79th Armoured Division in support of assaults. The bulldozers were produced in preparation for the Battle of Normandy with the tasks of clearing the invasion beaches of obstacles and quickly making roads accessible by clearing rubble and filling in bomb craters. As Allied armies advanced through Europe, the armored bulldozer was found to be too slow.There was a need for well-armored, obstacle clearing vehicle that was fast enough to keep up with tank formations. This need was met by various tank-mounted dozers such as the Centaur or Sherman.
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