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.

The Type II U-boat was designed by Nazi Germany as a coastal U-boat, modeled after the CV-707 submarine, which was designed by the Dutch dummy company NV Ingenieurskantoor voor Scheepsbouw Den Haag (I.v.S) and built in 1933 by the Finnish Crichton-Vulcan shipyard in Turku, Finland. It was too small to undertake sustained operations far away from the home support facilities. Its primary role was found to be in the training schools, preparing new German naval officers for command. It appeared in four sub-types.