Seeteufel (Sea Devil, also known as the Elefant (Elephant)) was a two-man amphibious midget submarine, developed by Nazi Germany during World War II. Only one prototype was built in 1944, although its testing was relatively successful and negotiations began for another series of three to test the necessary changes before beginning series production in 1945. These plans were cancelled at the beginning of that year when the decision was made to concentrate production on designs already being built.