Gustav Julius Werner Hartenstein (27 February 1908 – 8 March 1943) commanded the U-boat in the German Navy of the Third Reich during World War II. He received the Knight's Cross of the Iron Cross, a decoration awarded to recognise extreme battlefield bravery or outstanding military leadership. Corvette captain (or lieutenant commander) Hartenstein is credited with the sinking of 20 ships for a total of , and with damaging three ships and a destroyer.