M56 Scorpion
The M56 "Scorpion" Self-Propelled Gun is an American unarmored, airmobile self-propelled tank destroyer, which was armed with a 90mm M54 gun with a simple blast shield, and an unprotected crew compartment. History. 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 South Korea. With a crew of four (commander, gunner, loader and driver), the M56 weighed empty and combat-loaded. It had infrared driving lights but no NBC  protection 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 at 3,000 rpm, allowing a maximum road speed of and a maximum range of . Twenty-nine rounds of main gun ammunition were carried, and only the small 5 mm thick blast shield was armored. In service. 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-mobile, 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). As for foreign operators, Morocco was the only export customer which used M56 Scorpions in  actual combat. M56 Scorpions were deployed against Polisario rebels during the Western Sahara War. A number of examples were made available to South Korea but not used. Survivors. United States South Korea