Prior to Hitler's rise, Dr. Kurt Schimkus of Berlin worked on a "Death Ray" application that instead produced some form of mine-detonation device by 1931. It was taken out to Lake Constance and used against test mines. They all detonated within 600 ft!!! An amazing achievement... and yet there is no record of the Kriegsmarine ever using such a device at sea or mounted on German transport shipping during WW2! Schimkus worked in Berlin and later in the war Dr. Franz Phillip worked on a microwave weapon for the downing of aircraft (witness by U-boat commander Heinz Schaeffer in April 1945 under lab conditions and also shown to a Japanese delgation). Perhaps Schimkus' work was rejected in favor of microwave weapons instead. No further info. A pic of the lab device below from a peculiar source: Popular Science, Dec 1931 issue pg 17. Nothing more is known about this weapon. Not even by ME and I specialize in German Secret Weapons!!!

http://davidszondy.com/images/schimkus.png