Initially designated Piasecki Model 44, the H-21 Shawnee was the fourth tandem-rotor helicopter designed by Frank Piasecki, founder of the P-V Engineering Forum, later the Piasecki Helicopter Corp. After Piasecki left the enterprise in 1955, it became the Vertol Aircraft Corp. Boeing bought Vertol in 1960.

Originally designed for high-altitude, cold-weather operations, the first H-21s joined the U.S. Air Force in 1953 for rescue operations in the Arctic. The commercial transport version, the Vertol 44, was operated by several airlines. A total of 707 in the CH-21 series were built.