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M4
M4A1

18-ton High Speed Tractor M4^1-7

The high-speed tractor M4 was designed primarily as a prime mover for artillery loads weighing between 18,000-30,000lb (8,200-13,600kg). It could be used with the 3" antiaircraft gun mount M2A2; 90mm antiaircraft gun mounts M1A1 and M2; 155mm gun carriages M1, M2, and M3; 8-inch howitzer carriage M1; and 240mm howitzer carriage M1918. Cargo boxes for the different ordnances were interchangeable, and to avoid confusion it was encouraged that the vehicle be designated with the caliber of the weapon in parentheses. The cab was split into two compartments, with the front seating the driver and two crew and the rear seating eight more men on two facing rows of seats. The seat cushions were canvas zipper bags stuffed with blankets. A Gar Wood Model No. 4M718 winch was mounted at the rear under the ammunition box. It had a maximum pull of 30,000lb (13,600kg) with 300' (90m) of ¾" (1.9cm) cable. Full depression for the machine gun was only available to the front or rear. Tractors with serial numbers M4-1 to M4-300 were assembled with dual-wheel track return rollers, while tractors with serial numbers M4-301 and up featured single-wheel return rollers.

The M4 (90mm) had a series of pigeon holes in the ammunition compartment made of thin, flat metal strips that each stored one 90mm shell in a fiber container. If the tractor was to carry 90mm ammunition in steel packing cases, the pigeon holes were removed and angle iron strips were built into the compartment instead. When using steel packing cases, steel reinforcing angle irons were also welded to the rear of the ammunition compartment, and the rear door was welded shut.

The M4 (155mm or 240mm) featured a permanently-mounted crane, and its ammunition compartment had a large rear door. The M4C (155mm or 240mm) had extra ammunition racks installed in the rear cab, reducing the passenger capacity there to six men

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18-ton High Speed Tractor M4A1^1-3,7

The suspensions of the M4A1 and M4A1C were spaced out from the hull, allowing extended end connectors to be installed on both sides of the tracks. With the extended end connectors installed, the tracks were 23 11⁄16" (60.1663cm) wide. Otherwise, these were similar to the M4 and M4C. The M4A2 appeared in 1954, when Bowen-McLaughlin rebuilt and upgraded a number of the M4-series high speed tractors due to tight inventory of the newer cargo tractor M8.

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References

1. Hunnicutt, R.P. Bradley: A History of American Fighting and Support Vehicles. Navato, CA: Presidio Press, 1999. Reprinted with permission from Bradley, R.P. Hunnicutt ©1999, available from Presidio Press, 505B San Martin Drive, Suite 160, Navato, CA 94945.
2. Crismon, Fred W. U.S. Military Tracked Vehicles. Osceola, WI: Motorbooks International, 1992.
3. TM 9-785 18-ton High Speed Tractors M4, M4A1, M4C, and M4A1C. Washington, DC: Department of the Army, 18 April 1952.
4. TM 9-1785A Ordnance Maintenance--Engine, Engine Accessories, and Torque Converter for 18-ton M4 and 38-ton M6 High Speed Tractors. Washington, DC: War Department, 27 March 1944.
5. TM 9-1785B Ordnance Maintenance--Power Train, Suspension, and Equipment for 18-ton High Speed Tractor M4. Washington, DC: War Dept., 4 Apr 1944.
6. TM 9-2800-1/TO 19-75A-89 Military Vehicles (Ordnance Corps Responsibility). Washington, DC: Departments of the Army and Air Force, 13 February 1953.
7. Sola, Samuel, Vincent Bobkowski, and Kara Crocker. Weapon Mounts for Secondary Armament. Santa Monica, CA: G. O. Noville & Associates, Inc., April 1957.

Last updated 14 May 2023.
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