Two H-21B used for engine test, 1958-1960. Piston engine replaced by either one or two gas turbine engine of two different marks. Both later retrofitted with piston engines and delivered as UH-21B, 1962. 
List of Operators of H-21D |
| Years | Model | Org | |
|---|---|---|---|
| 1952/74 | H-21 |  US Air Force |
Global Distribution of H-21D |
|
Construction Numbers |
| C/N | Year | History | ||
|---|---|---|---|---|
| B-167 | 1958 | 57-2610 | ||
| B-168 | 1958 | 57-2611 | ||
