German submarine U-1003 was a Type VIIC/41 U-boat of Nazi Germany's Kriegsmarine during World War II.

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 BBC GG UB 720/8 double-acting electric motors producing a total of 750 metric horsepower (550 kW; 740 shp) for use while submerged.

[2] On 7 February 1944, during U-1003's trials, a crewman fell overboard and died while transferring to an outpost boat, near Hela on the Baltic Sea.

Fourteen Allied ships, from Escort Groups C-4, C-25, and C-26, began a massive search for the heavily damaged U-boat but U-1003 managed to elude them.

She then sat on the bottom for another 48 hours for repairs, however, on 23 March, the severe damage to the boat forced her crew to scuttle her off the coast of Ireland.