The experience of the Korean War led U.S. Army officials to begin the phasing out of the M24 Chaffee in favor of designs based around the more modern M41 Walker Bulldog. Included in the M24 family of vehicles was the M19 GMC.
Developed towards the end of the Second World War, the M19 was armed with two of the highly effective 40mm Bofors anti-aircraft guns, mounted in an open-topped turret capable of traversing 360°.
Since the 40mm Bofors was still considered an effective anti-aircraft weapon, the turret of the M19 was simply mated with chassis of the M41 to create the M42 - or Duster, as it became known as by troops serving in Vietnam.
The first M42s begun arriving in Vietnam during 1966, and as it become clear that the threat of North Vietnamese air power would never materialize, the M42 was quickly put to work in a ground-support role. With each gun capable of firing 120 rounds per minute, the 40mm rounds of the M2A1's Bofors proved devastating against both unarmored ground targets and massed infantry attacks.