Along with conventional U-boat operations Dönitz authorised clandestine activities in Canadian waters, including spying, mine-laying, and recovery of German prisoners of war (as Dönitz wished to extract information from rescued submariners concerning Allied tactics). All of these things tied down Canadian military power and imposed industrial, fiscal, and psychological costs. The impunity with which U-boats carried out these operations in Canadian waters into 1944 provided a propaganda effect. . One of these operations was the well-known Operation Kiebitz to rescue Otto Kretschmer.