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 Piasecki H-21D | |
| From | Organisation with model H-21D | |||||
| 1952 |
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| Construction Numbers on database of H-21D | ||||||
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Construction Numbers | Help Us | |
| C/N | Year | History | ||
| B-167 | 1958 |  57-2610 | ||
| B-168 | 1958 | 57-2611 | ||