The M52 was the tractor unit of the M39 series, the family of five-ton 6×6 tactical trucks that served the US armed forces from 1951 to 1969. Its job was to tow semi-trailers, and it appears in REO’s own list of products alongside the company’s M34, M35 and M109 military trucks. The series used a standard military cab designed by REO, with hinged doors, a folding windshield and a removable canvas roof.
REO M52 at a glance
| Series | M39 (G744) five-ton 6×6 |
|---|---|
| Role | tractor unit for semi-trailers |
| Production | 1951–1969 |
| Builders | International Harvester, Kaiser-Jeep, Diamond T, Mack; cab designed by REO |
| Original engine | Continental R6602, 602 cu in (9.9 l), 224 hp |
| A1 engine | Mack ENDT-673 turbo diesel, 210 hp |
| A2 engine | Continental LDS-465-1A multifuel, 175 hp |
| Transmission | Spicer five-speed manual, two-speed transfer case |
| Chassis | M61 short chassis, 167 in (4.24 m) wheelbase |
| Towing | 37,500 lb (17,000 kg) off-road, 55,000 lb (25,000 kg) on roads |
| Trailer | normally a 12-ton, two-axle trailer |
| Winch | optional 20,000 lb (9,100 kg) Garwood front winch |
The M52 is described in a section of the English Wikipedia article on the M39 series, which names International Harvester, Kaiser-Jeep, Diamond T and Mack as producers. REO’s own product list includes the M52, but REO’s part in the programme is not documented in the sources used here.
History of the REO M52
The M39 programme
The M39 series was designed as a five-ton three-axle all-wheel-drive off-road truck to replace the wartime four- and six-ton 6×6s of Brockway, Diamond T, Mack and White. International Harvester rushed it into production in 1951, Kaiser (renamed Kaiser-Jeep in 1963) soon became a major manufacturer, and Diamond T and Mack built smaller numbers. The series was the primary heavy truck of the US Army and Marine Corps during the Vietnam War and was also used by the Navy, the Air Force and South Vietnamese forces. It began to be replaced by the M809 series in 1970 and the M939 series in 1982, but continues to serve in other countries.
The tractor version
The M52 was one of several bodies on the same chassis, alongside the M54 and M55 cargo trucks and the M51 dump truck. Tractor trucks towed semi-trailers of up to 37,500 lb with 15,000 lb on the fifth wheel; on improved roads the figures rose to 55,000 lb and 25,000 lb respectively. Semi-trailer combinations had to stay on relatively flat ground and were not rated for full off-road use. They normally pulled a 12-ton two-axle trailer, in stake-and-platform, van, low-bed or tanker form, and there were also six-ton expansible and single-axle vans.
Cab, chassis and equipment
The tractors used the M61 short chassis, with 167 inches from the front axle to the centre of the rear tandem, one of three wheelbases in the series. All M39s had a ladder frame with three live beam axles on leaf springs, a Spicer five-speed gearbox and a two-speed transfer case that engaged the front axle automatically if the rear wheels slipped. The original petrol engine was the 602 cu in Continental R6602 of 224 hp; the A1 upgrade brought the Mack ENDT-673 turbo diesel of 210 hp and the A2 the Continental LDS-465-1A multifuel of 175 hp. Many trucks carried a 20,000 lb Garwood winch, which weighed 714 lb and added about 15½ inches to the length. Cargo trucks and tractors could be fitted with a ring mount for an M2 Browning machine gun.
Design and features
- Fifth-wheel tractor: built to haul semi-trailers rather than cargo, with 15,000 lb on the fifth wheel off-road.
- REO-designed cab: the standard military cab of the series, with hinged doors, roll-up windows and a folding windshield.
- Three engine generations: Continental petrol, Mack turbo diesel and Continental multifuel.
- Self-recovery winch: a 20,000 lb Garwood unit was a common fitting.
REO M52 versions
- M52: the standard tractor with the Continental R6602 petrol engine.
- M52A1: tractor with the Mack ENDT-673 turbo diesel.
- M52A2: tractor with the Continental LDS-465-1A multifuel engine.
- M51 dump truck: the same chassis with a five-cubic-yard dump body.
- M54 and M55 cargo: the standard cargo body and an extra-long version with a 20-foot box.
The smaller REO M35 was the two-and-a-half-ton truck of the same era, and REO’s pre-war cars such as the Royale are described separately. More vehicles are in the REO collection.
Sources
- M39 series 5-ton 6×6 truck, English Wikipedia: chassis, engines, tractor role, cab
- REO Motor Car Company, English Wikipedia: M52 in REO’s product list
