| U | U-505 (USA) | (Unnukka) (Finland) |
| U-1 (Germany) | U-521 (Canada) | Unterwalden (Switzerland) |
| U-3 (Sweden) | U-534 (GB) | Unyo Maru (Japan) |
| U-9 (Germany) | U-995 (Germany) | (Uranus) (Sweden) |
| U-10 (Germany) | (U-2540) (Germany) | (Urfahr) (Yugoslavia) |
| U-20 (Austria) | Uitto 6 (Finland) | Urger (USA) |
| U-111 (Netherlands) | (Ukiah) (USA) | Uri (Switzerland) |
| U-359 (Denmark) | Ukko-Pekka (Finland) | Uruguay (Argentina) |
| U-457 (GB) | Ulundi (South Africa) | Utah (USA) |
| U-461 (Denmark) | Undine (Germany) (New Zealand) | Utra (Finland |
| U-480 (Belgium) | Unicorn (GB) | Utrecht Ship (Netherlands) |
| U-484 (USA) | (Unicorn II) (GB) | Uurastaja (Finland) |
| United States (USA) |
