German submarine U-1233

German submarine U-1233 was a Type IXC/40 U-boat built for Nazi Germany's Kriegsmarine during World War II.

U-1233 was ordered in October 1941 from Deutsche Werft AG in Hamburg-Finkenwerder under the yard number 396. Her keel was laid down on 29 April 1943 and was launched on 23 December 1943. About three months later she was commissioned into service under the command of Korvettenkapitän Hans-Joachim Kuhn (Crew 31) in the 31st U-boat Flotilla.

After completing training and work-up for deployment U-1233 was transferred to the 33rd U-boat Flotilla for front-line service on 1 November 1944. The U-boat left Horten on 11 December 1944 for the first and only war patrol. After returning to Kiel, Kuhn was relieved as commander by Oberleutnant zur See Heinrich Niemeyer (Crew X/39) on 15 April 1945. In May 1945 'U-1233 transferred to Fredericia in order to surrender to Allied forces. En-route the U-1233 and two accompanying U-boats - GS U-155 (1941) and GS U-680 - were attacked by Allied aircraft. In the course of the attack one P-51 Mustang of No. 126 Squadron RAF was shot down.

In June 1945 the surrendered U-boats were transferred to Wilhelmshaven under British guard from where they sailed for Loch Ryan, a collecting point for Operation Deadlight. On 28 December 1945 U-1233 was towed to sea by HMS Freedom (W139). When the cable slipped the U-boat was sunk by artillery fire from HMS Onslaught (G04) on 29 December 1945 in position 54.85°N, -8.9°W