The 1st U-boat flotilla also known as the Weddigen flotilla, was the first operational U-boat unit in Nazi Germany's Kriegsmarine (navy). Founded on 27 September 1935 under the command of Fregattenkapitän Karl Dönitz, it was named in honor of Kapitänleutnant Otto Weddigen. Weddigen, a U-boat commander during World War I, died on 18 March 1915 after his submarine U-29 was rammed by the British battleship HMS Dreadnought in the North Sea.

German submarine U-9 was a Type IIB U-boat of Nazi Germany's Kriegsmarine. Her keel was laid down on 8 February 1935, by Germaniawerft in Kiel as yard number 543. She was launched on 30 July 1935 and commissioned on 21 August, with Korvettenkapitän Hans-Günther Looff in command.