M56 Scorpion

M56 Scorpion
M56 Scorpion preserved at the American Armored Foundation Tank Museum in Danville, Virginia.
Type	Self-propelled gun
Place of origin	United States
Service history
Used by	See users
Wars	Vietnam War, Western Sahara War
Production history
Manufacturer	Cadillac Motor Car Division of General Motors
Produced	1953–1959
Specifications
Weight	7.1 tonnes (16,000 lb)
Length	4.55 metres (14 ft 11 in) (excluding gun)
Width	2.57 metres (8 ft 5 in)
Height	2 metres (6 ft 7 in) over gun shield
Crew	4 (commander, gunner, loader and driver)
Armor	unarmored except for blast shield
Main armament	90 mm M54 Gun 29 rounds
Engine	Continental A01-403-5 gasoline engine 200 brake horsepower (150 kW)
Transmission	Allison CD-150-4, 2 ranges forward, 1 reverse
Suspension	Torsion tube over bar at wheels 1 and 4, torsion bar at wheels 2 and 3
Ground clearance	0.32 m (1 ft 1 in)
Fuel capacity	210 litres (46 imp gal; 55 US gal)
Operational range	230 kilometres (140 mi)
Speed	45 kilometres per hour (28 mph)

The M56 Scorpion was an unarmored American self-propelled anti-tank gun, which featured a 90mm M54 gun with a simple blast shield, and unprotected crew compartment. It was meant to be transported by helicopter or by air drop.

The M56 was manufactured from 1953 to 1959 by the Cadillac Motor Car Division of General Motors for use by US airborne forces, though the vehicle was eventually used by the Spanish Navy Marines, Morocco and the Republic of Korea as well. With a crew of four (commander, gunner, loader and driver), the M56 weighed 6.4 tonnes (14,000 lb) empty and 7.7 tonnes (17,000 lb) combat-loaded. It had infrared driving lights but no Nuclear, Biological and Chemical (NBC) protection system and was not amphibious.

The M56 was a fully tracked vehicle with rubber-tired run-flat road wheels and front drive sprocket wheels. It was powered by a Continental A01-403-5 gasoline engine developing 200 brake horsepower (150 kW) at 3,000 rpm, allowing a maximum road speed of 28 miles per hour (45 km/h) and a maximum range of 140 miles (230 km). Twenty-nine rounds of main gun ammunition were carried, and only the blast shield was armored.

The M56 saw combat service with U.S. forces in the Vietnam War. It was deployed with the 173rd Airborne Brigade, which was the only Airborne Brigade deployed with the M56, where it was used mainly in a direct fire-support role. Its function as an air portable, self-propelled, anti-tank vehicle was eventually replaced in Vietnam by the troubled but effective M551 Sheridan which had a fully armored turret. The USMC used the Ontos, which had an armored cabin and was armed with recoilless rifles, in a similar role (the running gear of the first Ontos prototype was the same as on the M56, but it was replaced for the production variant).