The Germans carried out a major anti-partisan operation in early June, Sturmwind I (German for 'Storm-Wind'). This operation, however, failed to defeat the partisans, who broke out of an encirclement in the Janów Forests (Lasy Janowskie) (according to some estimates, Germans suffered higher casualties than the resistance in Sturmwind I). Some partisan units moved to the Solska Wilderness and the Germans decided to start another operation - Sturmwind II - to eliminate them. By 15 June most of the Forest was surrounded; the partisan leaders assumed that the Germans would not enter it, but were proven wrong when on 21 June, after artillery and air bombardment, German forces started to advance.