The other submarine to be sunk was UB-116, which sailed from Heligoland on 25 October with special orders to attack the British fleet anchorage at Scapa Flow.[18] She was commanded by the 26-year-old Oberleutnant zur See Hans Joachim Emsmann[19] who, since first becoming a U-boat captain in February 1918, had sunk a total of 26 ships.[lower-alpha 9] She attempted to enter Scapa Flow submerged by the southern passage, Hoxa Sound, on the evening of 28 October. Hydrophones mounted ashore at Stanger Head, Flotta, alerted the British defenses, and the sea-bed magnetometer loops, designed to detect the magnetic signatures of incoming vessels[21] and thus trigger remote-controlled mines, were activated. Emsmann raised his periscope at 11:30 pm, presumably to check his position, and was spotted by look-outs on shore; the mines detonated shortly thereafter, leaving the submarine disabled on the sea bed.[22] She was finished off by depth charges from defense trawlers shortly thereafter; all 37 crew members were lost.[23][lower-alpha 10]