German submarine U-20 was a Type IIB U-boat of the Nazi German Kriegsmarine. Her keel was laid down on 1 August 1935, by Germaniawerft of Kiel as 'werk' 550. She was commissioned on 1 February 1936. During World War II, she conducted operations against enemy shipping. U-20 went on 16 war patrols, sinking 16 ships totalling 39,637 GRT and damaging one more of 1,846 GRT.