the careful fusing of mines laid as traps, their fuses desensitised to be activated only when the sweeping vessel was directly above them. Over one hundred vessels, mostly merchant ships of around and larger displacement, were converted as Sperrbrecher and it is estimated that around 50 percent of the vessels converted were lost during the war. During World War II only one commander received the Knight's Cross of the Iron Cross for services on a Sperrbrecher. Korvettenkapitän of the Reserves Karl Palmgreen received the award on 3 August 1941 as commander of Sperrbrecher IX and I. After the war some Sperrbrecher were converted back to merchant duties, a number remaining in service until the 1970s. See also R boat, for smaller German minesweepers M-class minesweeper (Germany) for larger German World War 2 minesweepers References Notes Bibliography Further reading External links Sperrbrecher, at German Navy website Mine warfare vessels of the Kriegsmarine World War II mine warfare vessels of Germany da:Minestryger#Sperbrecher de:Minenabwehrfahrzeug#Sperrbrecher