U
| Ship | Country | Class and type | Displacement (tons) | First commissioned | Fate |
| U-37 - U-44 | Germany | Type IX u-boats | 1,032 | ||
| U-65, U-66, U-103 - U-111, U-122 - U-124 |
Germany | Type IXB u-boats | 1,051 | ||
| U-66 - U-68, U-125 - U-131, U-153 - U-166, U-171 - U-176, U-501 - U-524 |
Germany | Type IXC u-boats | 1,051 | ||
| U-167 - U-170, U-183 - U-194, U-525 - U-550, U-801 - U-806, U-841 - U-846, U-853 - U-858, U-865 - U-870, U-877 - U-881, U-889, U-1221 - U-1235 | Germany | Type IXC/40 u-boats | 1,120 | U-877 sunk by HMCS St. thomas on 27 December 1944. All 56 members saved by crew of the St thomas. | |
| U-177 - U-182, U-195 - U-200, U-847 - U-852, U-859 - U-864, U-871 - U-876 | Germany | Type IXD u-boats | 1,616 | ||
| U-459 - U-464, U-487 - U-490 | Germany | Type XIV u-boats ("milch-kuh") | 1,668 | ||
| U-459 - U-464, U-487 - U-490 | Germany | Type XXI u-boats ("Elektroboote") | 1,668 | ||
| Uganda | UK | Fiji class light cruiser | 8,800 | 21 October 1944 | transferred to RCN as HMCS Uganda 21 October 1944, renamed Quebec 14 January 1952, scrapped 1961 |
| Underhill | USA | Buckley class destroyer escort | 1,673 | 15 November 1943 | sunk 24 July 1945 |
| Unicorn | UK | maintenance aircraft carrier | 16,510 | 12 March 1943 | scrapped 1960 |
| Unryū | Japan | Unryū class aircraft carrie | 17,150 | 6 August 1944 | sunk 19 December 1944 |
| Unyo | Japan | escort aircraft carrier | 17,830 | 31 August 1942 (ex merchant Yawata Maru) | Sunk 15 September 1944 |
| Utah | USA | Florida class battleship | 21,825 | 31 August 1911 | sunk 7 December 1941 |
Read more about this topic: List Of World War II Ships