Ships hit by U-21
See the profile page for U-21
| Date | U-boat | Commander | Name of ship | Tons | Nat. | Convoy | ||
| 21 Nov, 1939 | U-21 | Fritz Frauenheim |  | HMS Belfast (35) (d.) [Mine] | 11.500 |  | br | |
| 1 Dec, 1939 | U-21 | Fritz Frauenheim | | Mercator | 4.260 |  | fi | |
| 21 Dec, 1939 | U-21 | Fritz Frauenheim | Carl Henckel | 1.352 |  | sw | ||
| 21 Dec, 1939 | U-21 | Fritz Frauenheim | HMS Bayonet (Z 05) [Mine] | 605 | | br | ||
| 21 Dec, 1939 | U-21 | Fritz Frauenheim | Mars | 1.475 | | sw | ||
| 31 Jan, 1940 | U-21 | Wolf-Harro Stiebler | | Vidar | 1.353 |  | da | |
| 24 Feb, 1940 | U-21 | Fritz Frauenheim | Royal Archer [Mine] | 2.266 | | br | FN-100 | |
| 22.811 | ||||||||
| 6 ships sunk (11.311 tons) and 1 ship damaged (11.500 tons).
[Mine] indicates the vessel was hit by a mine laid by said U-boat.
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