The M939 truck was introduced in 1983, a Product Improvement Package upgrade of the M-809 series of 5-ton, 6x6 trucks. The M939s are general-purpose military vehicles, primarily designed for tactical, off-road use, with a top speed of 65 mph. The older fleet of M809 series tactical trucks were augmented by the M939 series without replacement.
M923 Truck, Cargo, 5-ton, 6x6, 6x6 Dropside, with machinegun ring mount, on a Somali road, between Mogadishu and Biadoa, Operation Restore Hope, 14 January 1993.
The M-939 Series 5-ton, 6x6 truck design was created by AM General Corp. who also built the M939 and M939A1 trucks. The M939A2 trucks, delivered starting in 1989, were produced by Bowen-McLaughlin-York.
The major improvements of the M939 Series vehicles over the M809 Series vehicles are as follows:
Over 30,000 of the M939 series trucks were delivered to the U.S. military. Of the many models in the M-939 series of 5-ton, 6x6 trucks, the most common in service were:
M923 Truck, Cargo
M925 Cargo Truck w/Winch
M927 XLWB Truck
M931 5-ton Tractor
M936 Medium Wrecker.
M927, M928, M934, and M945 model vehicles utilize the 215 in. (546.1 cm) Extra Long Wheelbase (XLWB) chassis to facilitate transporting of large and awkward loads
M923, M925, and M936 model vehicles utilize the 179 in. (454.7 cm) wheelbase
M929, M930, M931, and M932 model vehicles utilize the 167 in. (424.2 cm) wheelbase
Engines used for the M939 series were:
M939 & M939A1
655cid Cummins NHC 250
504.5cid Cummins 6CTA8.3
The M939 was fitted with 11:00R20 tires and tandem wheels on the rear axles while the M939A1 and M939A2 trucks were fitted with single rear wheels and larger 14:00R20 tires. Only the M939A2 vehicles are equipped with the centralized tire inflation system (CTIS).
The air brakes of the M939 series trucks are overly sensitive when the trucks are lightly loaded, empty, or when operating the vehicle on wet or slippery pavement. To rectify this problem, the military retrofitted these trucks with ABS brakes between 1999-2002.
Manuals for the M-939 series of 5-ton 6x6 trucks will be numbered TM 9-2320-272-xx where the xx represents the maintenance level. All together there are dozens of multi-volume manuals for the series of trucks.