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.

The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of 2,800 to 3,200 metric horsepower (2,060 to 2,350 kW; 2,760 to 3,160 shp) for use while surfaced, two AEG GU 460/8–27 double-acting electric motors producing a total of 750 metric horsepower (550 kW; 740 shp) for use while submerged.

[3] When submerged, the boat could operate for 80 nautical miles (150 km; 92 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 8,500 nautical miles (15,700 km; 9,800 mi) at 10 knots (19 km/h; 12 mph).

She was initially transferred to Loch Ryan, Scotland on 29 May 1945, and sunk on 8 December 1945 at 55°50′N 10°05′W / 55.833°N 10.083°W / 55.833; -10.083 as part of Operation Deadlight.