The US had learnt from WW2, that Airborne Divisions need the ability to tackle armoured vehicles, as they are dropped into and behind enemy lines. Tanks of the 1950’s proved to large and heavy to be deployed by airdrop with the Airborne Divisions. So a requirement was issued for an air deployable vehicle with enough punch to take on enemy armour.
The M56 entered service in 1953 as an air-deployable tank destroyer. It was equipped with a M54 90mm main gun as used on the M41 tank that had entered service the year before with the US Army.
Thou having the same the level of firepower as the M41 which weighted in at 45 tons, the M56 lacked the crew protection of a tank and weighted 7 tons. Thou the hull was constructed of aluminium, it offered no protection to the crew as it lacked a turret and just had a frontal gun shield, which gave limited protection for the gunner and loader. It wasn’t uncommon for the driver and commander to seek alternative cover from the vehicle when firing.
The vehicle used a Continental AOI-402-5 engine which generated 200hp and gave a range of 225km, with a top speed of 45km/h. The main gun could be traversed 30 degree’s left or right.
It saw action with the 82nd and 173rd Airborne Divisions in 1968 in the Vietnam War. Thou its not confirmed if it took on tanks or other AFV’s in direct contacts, it certainly engaged enemy forces in the fire support role. Despite a field modification, which replaced the M54 main gun with a M40A1 recoilless gun as used on the M50, the vehicle was replaced in service with the M551 Sheridan light tank.
The vehicle was also adopted by the Spanish and Moroccan Marine Corps.