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M56 (Scorpion) / (SPAT) Airborne Self-Propelled Anti-Tank Gun (1953)

Authored By Staff Writer | Last Updated: 12/2/2010

The M56 Scorpion was developed to provide American paratroopers with a mobile, self-propelled anti-tank weapon.

The M56 (also known as the "Scorpion" or "SPAT" = "Self-Propelled, Anti-Tank") was a fully-tracked, self-propelled anti-tank system mounting a formidable 90mm gun. The vehicle was specifically developed to give airborne troops (known as "paratroopers") a viable artillery component. Paratroopers became something of a normal operating entity within national armies during World War 2 - utilized to tremendous effect by the British, Germans and the Americans. As such, American authorities began development of the M56 in the 1950s and production ensued from 1953 into 1959 out of the Cadillac Motor Car Division of General Motors. The M56 went on to be used by airborne battalions and airborne infantry tank companies throughout the 1960s and could be airdropped by fixed-wing aircraft or precision-lowered into location via transport helicopter.

Hull construction of the M56 consisted of all-welded and riveted aluminum. The standard 90mm main gun utilized on the M56 chassis was closely associated with the main gun armament of the M47 "Patton" main battle tank. Twenty-nine projectiles of 90mm ammunition were carried aboard and the vehicle was crewed by four personnel made up of the driver, commander, loader and gunner. Power was derived from a single Continental A01-403-5 gasoline fueled engine delivering 200 horsepower. The transmission system consisted of an Allison CD-150-4 with two forward gears and a single reverse. Suspension was made up of a torsion tube over bar set at the 1st and 4th wheels while a torsion bar system was set at wheels two and three. Speed was roughly 28 miles per hour while range was limited to 140 miles. The vehicles operating weight was in the vicinity of 14,000lbs to 16,000lbs.

One of the obvious drawbacks of the M56 design was that the crew sat completely exposed to the elements and critically exposed to battlefield fire with the only protection being a forward blast shield behind the gun. The loader utilized a folding platform from which to position himself on when reloading the main gun. Despite the complete lack of crew protection, the system proved itself to be a formidable piece of mobile artillery particularly for those lightly armed combat forces that paratroopers generally were. Paratroopers were designed with speed and surprise in mind and thusly carried whatever tools of their deadly trade they required, jumping out of aircraft into the fray below ready for action. Couple this fact with the maximum allowable range of the main gun (set out to 1,500 meters) and the benefits more or less outweighed the M56's inherent design drawbacks. Another noted limitation of the M56 system soon lay in the main gun's recoil which would literally tilt the tank chassis up and rearwards when fired. This action also produced an absorbent amount of dust and smoke in the process, giving up the vehicle's location if the crew was attempting to remain hidden.

The M56 had an operational service life with both the United States 82nd Airborne and 101st Airborne divisions up until the 1960's before it was officially replaced in inventory by the new and improved M551 Sheridan - an "air-droppable" reconnaissance-minded light tank fitting a potent 152mm main gun. Even with the M551 formally online, the M56 Scorpion was still being fielded in limited numbers by the time of the Vietnam War though by now relegated to the fire support role as opposed to direct contact with enemy armor. The chassis of the base M56 was also be featured in several lesser-known US Army developments that included a dedicated armored personnel carrier, a mortar carrier and a recoilless rifle tank.

After the retirement of the M56 Scorpion SPG and the M551 Sheridan tank, US airborne divisions were essentially left without a dedicated self-propelled artillery piece in their inventory, a status which remains even today. Any remaining M56 pieces have become outdoor military museum mainstays for the viewing public. The 82nd Airborne War Memorial Museum located at Fort Bragg, North Carolina lays claim to one such display.

Beyond the US Army, Morocco and Spain were the only operators of the M56 system.

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Picture of M56 (Scorpion) / (SPAT)
Pic of the M56 (Scorpion) / (SPAT)
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Specifications for the
M56 (Scorpion) / (SPAT)
Airborne Self-Propelled Anti-Tank Gun

Country of Origin: United States
Manufacturer: Cadillac Motor Car Division of General Motors Corp - USA
Initial Year of Service: 1953
Production: 500

Focus Model: M56 (Scorpion) / (SPAT)
Crew: 4

Overall Length: 19.03ft (5.80m)
Width: 8.43ft (2.57m)
Height: 6.56ft (2.00m)
Weight: 7.9 US Short Tons (7,144kg; 15,750lbs)

Powerplant: 1 x Continental AOI-402-5 6-cylinder 4-cycle opposed fuel-injected gasoline engine generating 200hp @ 3,000rpm.

Maximum Speed: 28mph (45 km/h)
Maximum Range: 143 miles (230 km)

NBC Protection: None
Nightvision: None

1 x 90mm main gun

29 x 90mm projectiles

T101 - Prototype Systems as built by Cadillac Motor Car Division of which two were produced.

M56 - Standardized Production Model Designation based on the T101 prototype.

Morocco; Spain; United States