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

The submarine was powered by two MAN M 9 V 40/46 supercharged four-stroke, nine-cylinder diesel engines producing a total of 4,400 metric horsepower (3,240 kW; 4,340 shp) for use while surfaced, two Siemens-Schuckert 2 GU 345/34 double-acting electric motors producing a total of 1,000 shaft horsepower (1,010 PS; 750 kW) for use while submerged.

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 on 22 March 1944.

After returning to Kiel, Kuhn was relieved as commander by Oberleutnant zur See Heinrich Niemeyer (Crew X/39) on 15 April 1945.

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.