SM U-3 was the third German U-boat built by the Imperial German Navy. Launched in March 1909 and commissioned later in the year, the boat was the first of two submarines in its class. The boat was built by Kaiserliche Werft Danzig.
On 17 January 1911, U-3 sank in Heikendorfer Bay near Kiel harbour due to an open ventilation shaft valve. Its entire 30-man crew was rescued by SMS Vulkan via U-3s torpedo tube. Amongst the crewmen who were saved were Otto Weddigen, the later commander of , and Paul Clarrendorf, the commander of U-boot-Abnahme-Kommando in Kiel which enlisted U-boat crews.
During World War I the boat was used for training and did not see active service. At the end of the war it was surrendered and was being towed to Preston to be broken up when she sank.