Mary Seymour
| Name | Mary Seymour |
| Type | Sailing vessel |
| GRT | 150 tons |
| Country |  British |
| Built | 1865 |
| Builder | Tredwen, Padstow |
| Operator | B. M. Harvey, Plymouth |
| History | Wooden schooner. |
U-boat attacks on Sailing vessel Mary Seymour
| Date | U-boat | Loss type | Position | Location | Route | Cargo | Casualties | |
| 1 | 10 Sep 1917 | UC 51 (Hans Galster) | Sunk | Stopped and sunk 7 miles NNE of the Pendeen LH at 11:30am | 50.16N, 05.39W | Ellesmere Port - Cherbourg | coal | 0 |
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