Undine

U-class submarines were conceived as unarmed targets for anti-submarine training, but after the project had been approved, a decision was made to arm them with torpedoes. The fore-end was redesigned to accommodate six torpedo tubes. The submarines relied on electric motors to move, and they used diesel engines as generators. When World War II broke out, Undine participated in missions as part of the 6th Submarine Flotilla. On January 7, 1940, she was sunk by German auxiliary minesweepers.