This was a German and Croat operation against the partisan forces of Josip Broz Tito in the area to the north of the Sava river in Axis-occupied Yugoslavia (8/25 July 1943).
The object of the operation was the neutralisation of the partisan forces (12th Division and ‘Kalnik’ Partisan Detachment) along the railway connection linking Zagreb and Belgrade, and in the Kalnik mountain region between Varaždin and Križevci. There is some dispute as the size and composition of the German forces involved: some accounts indicate elements of Generalleutnant Willibald Utz’s 100th Jägerdivision, Generalleutnant Karl Eglseer’s 114th Jägerdivision, Generalleutnant Emil Zellner’s 373rd Division (kroatisch), Generalleutnant Josef Brauner von Haydringen’s 187th Reserve-Division, and the 92nd Grenadierregiment (mot.) of Generalmajor Hans-Adolf von Arenstorff’s 60th Division, while others indicate 4,000 German troops (with air support) furnished by the 462nd Grenadierregiment and the 1st Kompanie of the 202nd Panzerabteilung. The Croat contribution was the Combat Group ‘Peričić’ of Pukovnik Stjepan Peričić’s 1st Division, 3/2nd Regiment, six or seven Ustaše companies, and 12 light tanks.
After two weeks of only the most sporadic combat, the partisans withdrew to the south-east from the Kalnik mountain region into the Bilo mountain region.
According to the Germans, who admitted the loss of six men killed and 20 wounded, the Croats lost 40 men killed, 61 wounded and 66 missing, and the partisans 2,350 men counted dead and 84 taken prisoner. It should be noted that there was so much fighting in the area to the north-east of Zagreb during July 1943 that it is difficult to break down and determine exactly what the figure of 2,350 dead signifies: there is no reference to massacres, so the figure is probably the Axis claim for all partisan dead in the area to the north-east of Zagreb between 8 and 25 July, and not just those in the Kalnik mountain region.