Estrella WarBirds Museum

Cletrac Towing Memphis Bell

The M2 High-Speed Tractor (HST) was manufactured by the Cleveland Tractor Company for the U.S. Army Ordnance Department. Termed an MG-1+ by Cletrac, 8,510 were manufactured during World War II, primarily for use on airfields as a tow tractor and maintenance vehicle. Powered by a 404cid Hercules WXLC3 engine driving a 4-speed transmission, the vehicle is capable of attaining speeds up to 22mph when the high rpm range is unlocked on the governor, allowing the engine to achieve 3,250 rpm. With the governor set at 2,500rpm, speeds up to 15 mph can be attained. Steering is accomplished through a Cletrac controlled differential that uses planetary gearsets to “downshift” one track when the corresponding steering lever is pulled. In this way, power is always being transmitted to both tracks making the steering action smoother and improving safety on steep slopes. Compared to the traditional “clutch and brake” steering found on most other crawlers of this vintage, the Cletrac differential has the disadvantage that it is not possible to lock one track and spot-turn around the braked track. Instead, the minimum turning radius is 10.5 ft. While this was a disadvantage for bulldozers, the controlled differential did prevent the tractor from tearing up pavement and turf, keeping the surface smooth for aircraft operations.

The M2 is equipped with a swinging drawbar designed for use in towing aircraft, as well as a second, swiveling pintle hook for towing ammunition, maintenance, & other types of trailers. Some testing was done to determine the suitability of the M2 as a gun-towing tractor, but it was quickly determined that it lacked the space to support the gun crews and carriage of ammunition and, as a 7-ton class machine, it was too light to pull the heavier howitzers and was eclipsed in this role by the M4 13-ton HST, M5 18-ton HST, and the M6 38-ton HST. However, with rubber tracks that were suitable for use on paved surfaces as well as grass and mud, the tractor performed well on the primitive airfields that were common in forward areas during the war.

For servicing aircraft, the M2 was equipped with a variety of equipment, including a 110 VDC 3 kW generator mounted on the right, front fender and a 2-stage, intercooled, PTO-driven air compressor mounted behind the operator’s seat. The compressor supplied air at 1,000 psi to an air receiver tank mounted on the left fender that had regulators & a booster pump to supply air at 1,500 psi, 1,000 psi, or 150 psi. The 150 psi tap was used for powering air tools, while the higher pressure sources were for charging the aircraft landing gear oleos. Likewise, the generator, which was driven off of a front-mounted PTO gearbox that also powered the 7,500 lb winch, provided the electricity to start the aircraft, eliminating the need for a separate “start cart.” The vehicle is also equipped with (3) spotlights—(2) forward, (1) rear—that double as driving lights, as well as blackout-type marker lamps.