The H-21 used the same basic configuration as the HRP-2. The 41 foot rotor was increased to 44 feet, and a 1,425 horsepower engine installed, increasing the gross weight from 7,255 to 14,700 lbs. The H-21A was the winner of an air force design competition, designed as a high altitude arctic rescue helicopter for fourteen troops or twelve stretchers. Later versions (H-21B/C) were developed to lift 20 troops. The H-21 had a fixed tricycle landing gear with an all-terrain alighting capability using doughnut-shaped floats fitted around the wheels.
| Mission | Transport and Rescue |
| Crew | 2 |
| Passengers | 20 or 12 Liters |
| Engine | Wright R-1820 |
| Horsepower | 1,425 |
| Rotor Diameter | 44 ft |
| Fuselage Length | 52.6 ft |
| Weight Empty | 9,148 lb |
| Useful Load | 5,556 lb |
| Maximum Speed | 125 mph |
| Cruising Speed | 101 mph |
| Range | 150 mph |
| Ceiling w/ Normal Load | 7,750 ft |
Twin vertical fins were fitted at the tail. One H-21D had two T-58 turboshaft engines installed, married to a common transfer case; another had two T-53 turbines installed. The H-21 became the French army’s prime workhorse throughout the Algerian war, pioneering troop air assault tactics and a forward air supply system. The first helicopters to use .50 caliber machine guns in combat were the H-21’s in Algeria. Later, it was utilized in similar manner by the U.S. army in the early stages of the Vietnam war.
In 1953, the U.S. air force set two world records in the H-21; 146.7 mph speed and 22,110 feet altitude. On 24 August 1956, a U.S. army H-21 made the first non-stop transcontinental helicopter flight across the United States with inflight refueling in 37 hours.
Production of the H-21 totaled 707 for U.S. services including 150 for use in West Germany, Canada, France, Sweden, Japan and other foreign countries. Over 37 years later, some of these aircraft are still in service.