M6 Tractor
The M6 High-Speed Tractor was an artillery tractor used by the US Army during World War II. Manufactured by Allis-Chalmers, it was used to tow heavy artillery pieces, such as the 8-inch Gun M1 and 240 mm howitzer M1. Its G-number was (G-184). Development. Although in the late 1930s the US Army lacked a clear mechanization policy, the success of the "blitzkrieg" in 1939-40 highlighted the need of motorized vehicles for both tactical and strategic maneuver, which meant that towed artillery would need to move at a speed comparable to that of the  armored fighting vehicles. To achieve this, a series of “high speed tractors” was planned, which would tow the different artillery pieces existing (or planned) in the US Army inventory. The “high” speed was considered in comparison with horse-drawn artillery rather than that obtainable with wheeled prime movers or ballast tractors. The models considered in the series included: 7 ton, 13 ton, 18 ton, and 38 ton. Intended to tow heavy artillery pieces as the 240 mm howitzer M1 and the 8-inch Gun M1, the M6 artillery tractor was larger and heavier than the M4 Artillery Tractor, although they  had a similar layout. The main differences between both were in the following areas: It was powered by two six-cylinder, in-line, Waukesha 145GZ gasoline engines with an engine displacement of , each of which gave at 2,100 rev/min. The running gear consisted on six rubber-rimmed wheels per side, with the drive wheel located at the front and a large tensioning wheel at the rear; a layout similar to the one used in the M3 Light Tank and later in the M4 Tractor. Service history. The M6 tractor was chiefly used in the European theater only in the  last months of World War II. Until then large caliber artillery was moved by the M1 Heavy Tractor, heavy trucks, or vehicles such as the M33 Prime Mover, M34 Prime Mover or M35 Prime Mover derived from the M3 Medium Tank, M4 Medium Tank, and M10 GMC hulls respectively Use of this tractor in the Pacific theater seems to have been limited to training at Oahu, (Hawaii). Some vehicles were sold to Israel after being replaced by self-propelled artillery. Surviving vehicles. National Military Vehicle Museum, Edinburgh, South Australia