Hydra
| Name | Hydra |
| Type | Sailing vessel |
| GRT | 174 tons |
| Country |  Danish |
| Built | 1901 |
| Builder | J.A. Petersen, Mastal |
| Operator | C.W. Clausen, Marstal |
| History | Three-masted wooden schooner. |
U-boat attacks on Sailing vessel Hydra
| Date | U-boat | Loss type | Position | Location | Route | Cargo | Casualties | |
| 1 | 19 Sep 1917 | U 94 (Alfred Saalwächter) | Sunk | Sunk by gunnery W of the Orkneys | 59.33N, 07.37W | Swansea - Copenhagen | coal | 6 |
| Crew not recovered; vessel posted as missing. | ||||||||
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