This was the Allied release to the partisan forces of Marshal Josip Broz Tito in German-occupied Yugoslavia of intelligence that would facilitate the launch of an interdiction campaign against German road and rail communications north through Slovenia (May/June 1944).
The object of the campaign was to prevent German forces from being moved from the Balkans in anticipation of the Allied landings in North-West Europe during 'Overlord'.
During the night of 25/26 May a senior liaison officer of the Special Operations Executive, Lieutenant Colonel Peter Moore, returned from Bari in south-eastern Italy to the Yugoslav partisan general staff in Slovenia to arrange this interdiction campaign against German road and rail communications northward through Slovenia with the objective of halting all German movement through the region to prevent reinforcements from Balkan going to either France after 'Overlord' or to Italy, where the Allies were preparing a major offensive. For the purpose 38 tons of explosives were paradropped to the partisans in Slovenia.
The operation proper started on 7/8 June with sabotage of the railway linking Trieste and Ljubljana, followed by the destruction of the Štampet bridge on 12/13 June. Two more bridges were destroyed on 17/18 June. Sabotage undertakings on the lines of communication between Ljubljana and Zagreb, and between Maribor and Celje on 20/21 June halted German traffic until 20 July. Major Franklin Lindsay of the Office of Strategic Services reported a significant drop in German rail traffic between 7 and 20 June.
The success of 'Bearskin' confirmed that larger operations were possible, and this led to 'Ratweek'.