The US Army began accepting deliveries of the M42 in October 1952, and when production ended in 1959, approximately 3,700 units had been delivered. By the late 1960s, the Duster's limits seemed to have been reached. The lack of a radar tracking system meant the M42 was a "fair weather" shooter against low, slow targets; it just could not keep pace with the new generation of Soviet jet aircraft. As US involvement in Vietnam increased, three battalions of Dusters were sent to South Vietnam, initially for anti-aircraft duties, but with clear skies over the South, the M42 was usefully employed as convoy escort, perimeter and base security, and direct-fire support.