Military Vehicle Spotlight: GMC M135 6x6 2-1/2-ton Truck

Specifications

GMC 302 engine left front view TM 9-8025-1 Ordnance Field and Depot Maintenance GMC Model 302 Engine

Weight: 12,330 pounds
Size (LxWxH): 269" x 88" x 105"
Engine: GMC 6-cylinder 302 cu. in.
Transmission: (early) GMC 302M Hydro-Matic (later) 303M. Automatic, 4 speeds and 2 ranges, with a single range transfer case
Horsepower: 130@ 3,200 rpm
Electrical: 24-volt
Wheelbase: 180 inches
Tires: six 11.00-20
Max Speed: 58 mph
Range: 300 miles

History

Ronald Boltz shot this photo of an M135 in Vietnam.

When Reo Motors with its G-742 (M34/M35 cargo trucks) was selected as the prime contractor for the “interim” series of trucks to replace the Army’s aging fleet of CCKWs in 1949, GMC was dismayed. The company responded by submitting a prototype of its own design, built with corporate money, as an alternative. In its original form it had much in common with the CCKW, and this was a much-touted advantage. Many of the repair parts were already in place in the Army’s supply channels and a minimal amount of new training would be required for mechanics.

Sonny Hanson's 1952 M135 fitted with the Arctic kit. John Adams-Graf photo

Its most radical departure from the previous generation of vehicle was the installation of GM’s Hydramatic transmission. The transmissions in these trucks had a rear pump. This allowed the truck to be pull-started in a conventional manner, something that can’t be done with today’s automatics.

The earliest trucks, the M135s, had 11.00-20 single rear tires for improved off-road performance.

The transmissions in the very first trucks shipped to Korea during that war were deficient. These problems were almost immediately corrected, but not before the transmissions earned an unwarranted reputation that lingers to this day.

Though these trucks did not garner the widespread acceptance with the U.S. Army that GM had hoped for, they did with the Canadian armed forces, where they formed the backbone of military transport for more than 30 years.