German submarine U-1223 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 Kapitänleutnant Harald Bosüner (Crew 35) on 6 October 1943 in the 4th U-boat Flotilla.

While working up for deployment, U-1223 Bosüner was relieved and handed over command to Oberleutnant zur See Albert Kneip (Crew X/39) in March 1944.

Stopping briefly in Bergen, Norway, for replenishment, she operated off the Canadian coast, damaging HMCS Magog on 14 October 1944 and the British steamer Fort Thompson on 2 November.