The M56 Scorpion was born out of the need for an air-transportable anti-tank gun. Its design was kept as simple as possible and essentially consisted of a 90-mm M54 gun protected by a simple blast shield, while sharing some characteristics with the chassis of the M76 amphibious load carrier. The hull was constructed of welded and riveted aluminum, with engine at the front, gun in the center, and a loading area in the rear. Aside from the gun shield, the rest of the hull was unarmored, and offered practically no protection against small arms fire or shell fragments. However, its firepower was considerable, thanks to the 90-mm M54 gun which was a derivative of the gun used in numerous late- and post-war tanks and tank destroyers (its ammunition was similar to the one used in the M48). Additionally it lacked an NBC system as well as amphibious capability although it was capable of fording under preparation. The tracks were a continuous rubber band with reinforced steel steel, and the road wheels were conventional rubber tires as well. Its only combat service with the US Army came during the Vietnam War, where it was in use by the 173rd Airborne Brigade, but was eventually replaced by the M551. Other export customers included Spain and Morocco.

A 1948 requirement for a light self-propelled anti-tank gun capable of being transported by air and helicopter resulted in the T101 and T101E1 prototypes. These eventually resulted in the M56 of which only the basic variant was built although further prototypes were developed.