The United States went to war in Korea in 1950 following the invasion of the democratic South by the communist-backed North, spawning the Korean War that - at least on paper - lasted from 1950 to 1953. Such a war environment served to dictate the short-term needs of any army and, accordingly, American authorities began to phase out their World War 2-era M24 "Chaffee" light tank and all its related derivatives to concentrate production of new derivatives based on the newer M41 "Walker Bulldog" light tank. The M41 light tank began development in 1947 and production ensued in 1953 to directly replace the outmoded M24. The M24 proved successful enough for her time but the new wars being waged dictated a modernized weapon system that would feature both improved armor protection and firepower.
One offshoot of the original M24 light tank family became the "M19 Gun Motor Carriage" self-propelled, anti-aircraft platform mounting a pair of 40mm Bofors cannons in an open-topped traversing turret. While the M24 chassis it was built upon was no longer a viable solution to the revamping American Army, the turret system and its 40mm guns were still an effective short-ranged deterrent against low-flying enemy aircraft. As such, the decision was made to simply relocate the existing M19 turrets and their applicable arms to the newer all-welded steel hulls of the M41 Walker Bulldog light tanks - in effect creating an updated anti-aircraft weapon system and the new designation of "M42".
The M42 was powered by a single 6-cylinder air-cooled gasoline fueled engine with 500 horsepower output. Primary armament was the aforementioned pair of 40mm M2A1 Bofors anti-aircraft cannons with a single 7.62mm M1919A4 general purpose machine gun (or later, the M60 GPMG) fitted as secondary. The cannons would initially be tied to a radar-guided fire control system but this option was eventually dropped in lieu of ballooning project costs. Each cannon maintained a hefty rate-of-fire of 240 rounds per minute with a fully automatic firing action. As the M42 was based on the M41 light tank chassis, she reflected much of the latter's qualities including the torsion bar suspension, a well-sloped glacis plate and five road wheels per track side. Operational range for the M42 was listed at approximately 100 miles with a top speed nearing 45 miles per hour. Operational weight was in the vicinity of 49,500lbs. A standard operating crew would be between four and six personnel to include the driver and gunnery specialists.
The M42 entered production in 1952 out of the Cleveland Tank Plant of General Motors and entered service the following year. Production continued on through 1959 to which some 3,700 vehicles were delivered to the US Army and others. As missile technology advanced ever further in the burgeoning jet age, it became a common viewpoint that self-propelled anti-aircraft guns such as the M42 had already seen their best days. As such, the type was subsequently removed from active frontline service within time beginning in 1963, replaced by more modern advanced missile-minded systems such as the MIM-23 HAWK - a tracked surface-to-air, medium-range deterrent.
The United States had already been involved in low-key activities in Vietnam since 1950. By the early 1960s, involvement was ramping up and full military combat deployments were taking place beginning in 1965. The HAWK missile system was therefore deployed to the region to protect allied ground interests from incoming low-level enemy air attacks. However, the HAWK proved to have a weakness against such targets at that range and the M42 was therefore reactivated and deployed during the Vietnam War to shore up air defense limitations. These M42s - upgraded with new engines to become the M42A1 - were assigned to three battalions belonging to the Air Defense Artillery detachment. At some point during its career, the M42 came to known as the "Duster" by American servicemen.
The Duster system provided little useful air defense service in the early going as the massed threat from low-flying North Vietnamese aircraft was not to be. Spares were hard to come by and maintenance requirements proved high for the aging weapon. Consequently, M42s were committed more and more to the ground support role where their dual rapid-firing 40mm cannons could be brought to bear against a dug in enemy or against troop concentrations and soft-skinned vehicles. In fact, Dusters proved quite exceptional in the role and went on to provide armed escort to convoys as well as guard American bases from air or ground assault from North Vietnamese elements. After the last M42 teams left Vietnam proper, Dusters stocked the ranks of the US National Guard until the type was formally and finally retired from operational service in 1988.
Key variants of the M42 family line included the original production M42 followed by the upgraded M42A1 which was nothing more than an M42 with an AOSI-89505 series 500 horsepower engine (among other subtle refinements). "Type 64" was a designation used by the Taiwanese Army for a light tank that melded the open-topped turrets of obsolete World War 2-era M18 "Hellcat" tank destroyers with existing hulls of M42s. Similarly, Venezuela developed an indigenous self-propelled anti-aircraft system by fitting existing M42A1 turrets with French AMX-13M51 light tank tracked hulls to create the AMX-13/M41E1 "Rafaga".
While the M42 was never a unanimous export success, she did find a home outside of the American military for she went on to stock the inventories of the West German, Greek and Japanese armies as well as those of Lebanon, Taiwan, Thailand, Turkey, Jordan, Venezuela and Pakistan. Pakistan may still maintain some 100 examples in active service.