Production of the Clarktor-6 began in 1942 and ended in 1966.Between 1941 to 1945, CLARK produced almost 90 percent of the military requirements for fork lift trucks and tow tractors. During WWII  there was not an air field under Allied control that did not have a CLARK tow tractor. The Clarktor 6 was powered by a water-cooled Chrysler six-cylinder 230-cid flathead gasoline engine of 6 2hp, with a three-speed gearbox that could reach a maximum speed of 15 mph. Production began in 1942, and by the end of the war Clark had delivered thousands of different cargo handling vehicles, including an order for more than 1,500 Clarktor 6s for the British Royal Air Force. These were built as a version designated “BH”, standing for ‘British Heavy’, and supplied to Ministry of War Transport for the RAF under the Lend Lease Act. Mill-33 is the lighter variant of the tug,  with single rear wheels, and a drawbar capacity of over 2 tons and a towing capacity of 90 tons, allowing it to handle all types of  bomb trailers and aircraft, including the heavy bomber aircraft in service with the USAAF and the RAF.