The M809 5-ton, 6x6 trucks were manufactured between the years 1969 and 1982, by Kaiser Jeep, who later became AM General. By the end of production there were approximately 92,000 M809s designed. In the 1960s, the U.S. Army wanted to replace the standard multi-fuel engines with diesel engines. The M809 series was an upgraded version of the 5-ton M39 series, in turn had an upgraded version named the M939 series, and then eventually the M939 series were slowly replaced with the Medium Tactical Vehicles (MTV) starting in 1991. Even though, all the trucks were upgrades of each other, they were still mechanically similar in design. The M809 series and its variants were designated as G908 by the U.S. Army Ordnance Corps Supply Catalog. The main function of the M809 trucks were to transport troops, cargo and materials over any type of terrain, with up to 5-tons (10,000lbs (4,500 kg)) and in most cases doubling the load size.
The M809 series had 3 wheelbases: short, standard long and extra-long. At 14ft 11in (4.55m), the M809 was considered the “standard long wheeled”. The M810 was the “short wheeled” at 13ft 11in (4.24m). The M811 and M812 were the “extra-long wheeled” at 17ft 11in (5.46m). The M809 series had a ladder frame with 3 axles. The front axle was on semi elliptical leaf springs and the rear tandem on quarter elliptical leaf springs. The M809 was lengthened in the hood, frame and fenders compared to the M39. This was to make room for the only engine used in the M809s which was a 240hp Cummins NH250, naturally aspirated diesel engine. A Dana-Spicer manual, 5-speed, synchromesh transmission with a Rockwell-Standard 2-speed transfer case that engaged the front axle was used. The brakes were air over hydraulic with drum brakes on all the wheels. Variants that used a trailer, used air brake connections that were separate from the service brakes. The M809s had a redesigned grille and an air cleaner on the left front fender. They also had a rear pintle hitch which could tow 15,000lb (6,800kg) trailers and a front mounted 20,000lb (9,100kg) capacity winch.
Since this series did not have any engine upgrades or transmission upgrades all the M809 variants were based on the wheelbase lengths and main operation of the vehicle. The M813 & M814 were cargo trucks. The M815 was a bolster truck. The M816 and M819 were wrecker/recovery trucks. The M817 was a dump truck. The M818 was a tractor. The M820 had an expansible van body and the M821 was a bridge transporter.