area B 25 September 1918 sunk by the North Sea mine barrage area A September 1918 presumed sunk by the North Sea mine barrage area B (confirmed in 2006) 19 September 1918 sunk by the North Sea mine barrage area B September 1918 unknown - possibly sunk by the North Sea mine barrage 18 October 1918 sunk by the North Sea mine barrage area A Eight more boats were known to have been damaged by the mines and some Admiralty personnel assumed the field might be responsible for five more U-boats which disappeared without explanation. Cleanup United States participation in the minesweeping effort was overseen by Rear Admiral Strauss aboard the repair ship Black Hawk, from which he had commanded the minelaying operation. Tugs and towed Admiralty wooden sailing smacks Red Rose and Red Fern out to conduct the first trial sweep in December. Sweeping was accomplished by suspending a serrated wire between two ships on a parallel course. While held underwater by planing devices called "kites", the wire would foul the cables suspending the buoyant mines above their anchors. If the serrated wire parted the mine mooring cable, the mine would bob to the surface to be destroyed by gunfire. The smacks swept and destroyed six mines before winter weather halted further work at sea. The winter was spent testing an electrical protective device to reduce the risk of sweeping the antenna mines with steel-hulled ships. Patapsco and Patuxent tested the protective device by sweeping 39 mines in March. Royal Navy minesweeping efforts involved 421 vessels manned by 600 officers and 15,000 men from 1 April to 30 November 1919. Twelve Lapwing class minesweepers and 18 submarine chasers were available for the first routine sweep of the United States minesweepers on 29 April 1919. After the first sweep took two days to clear 221 mines, Strauss requested more ships in the hope of clearing the mine barrage that summer. Twenty Admiralty trawlers with American crews, 16 more Lapwing class minesweepers, and another repair ship were assigned to his command. Panther was given responsibility for tending trawlers William Ashton, Thomas Blackhorne, Thomas Buckley, Richard Bulkeley, George Burton, Pat Caharty, William Caldwell, George Clarke, John Clay, George Cochrane, John Collins, William Darnold, Sam Duffy, John Dunkin, John Fitzgerald, John Graham, Thomas Graham, Thomas Henrix, William Johnson, Thomas Laundry, and submarine chasers SC-37, 38, 40, 44, 45, 46, 47, 48, 95, 110,