German submarine U-1203 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 15 May 1943 by Schichau-Werke, Danzig as yard number 1573, launched on 9 December 1943 and commissioned on 10 February 1944 under Oberleutnant zur See Erich Steinbrink.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-1203 had a displacement of when at the surface and while submerged. She had a total length of , a pressure hull length of , a beam of , a height of , and a draught of . The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of for use while surfaced, two AEG GU 460/8âÂÂ27 double-acting electric motors producing a total of for use while submerged. She had two shafts and two propellers. The boat was capable of operating at depths of up to .
The submarine had a maximum surface speed of and a maximum submerged speed of . When submerged, the boat could operate for at ; when surfaced, she could travel at . U-1203 was fitted with five torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one SK C/35 naval gun, (220 rounds), one Flak M42 and two twin C/30 anti-aircraft guns. The boat had a complement of between forty-four and sixty.
The boat's career began with training at 8th Flotilla on 10 February 1944, followed by active service on 1 December 1944 as part of the 11th Flotilla.
U-1203 took part in no wolfpacks.
U-1203 surrendered on 9 May 1945 in Trondheim. She was initially transferred to Loch Ryan, Scotland on 29 May 1945, and sunk on 8 December 1945 at as part of Operation Deadlight.