<P> The first submarine built in Germany, the three - man Brandtaucher, sank to the bottom of Kiel harbor on 1 February 1851 during a test dive . The inventor and engineer Wilhelm Bauer had designed this vessel in 1850, and Schweffel & Howaldt constructed it in Kiel . Dredging operations in 1887 rediscovered Brandtaucher; it was later raised and put on historical display in Germany . </P> <P> There followed in 1890 the boats WW1 and WW2, built to a Nordenfelt design . In 1903 the Friedrich Krupp Germaniawerft dockyard in Kiel completed the first fully functional German - built submarine, Forelle, which Krupp sold to Russia during the Russo - Japanese War in April 1904 . The SM U-1 was a completely redesigned Karp - class submarine and only one was built . The Imperial German Navy commissioned it on 14 December 1906 . It had a double hull, a Körting kerosene engine, and a single torpedo tube . The 50% - larger SM U-2 (commissioned in 1908) had two torpedo tubes . The U-19 class of 1912--13 saw the first diesel engine installed in a German navy boat . At the start of World War I in 1914, Germany had 48 submarines of 13 classes in service or under construction . During that war the Imperial German Navy used SM U-1 for training . Retired in 1919, it remains on display at the Deutsches Museum in Munich . </P> <P> On 5 September 1914, HMS Pathfinder was sunk by SM U-21, the first ship to have been sunk by a submarine using a self - propelled torpedo . On 22 September, U-9 sank the obsolete British warships HMS Aboukir, HMS Cressy and HMS Hogue (the "Live Bait Squadron") in a single hour . </P> <P> In the Gallipoli Campaign in early 1915 in the eastern Mediterranean, German U-boats, notably the U-21, prevented close support of allied troops by 18 pre-Dreadnought battleships by sinking two of them . </P>

When were u boats first used in ww1