'Varazdin' was a German and Croat operation, together with 'Paula' (ii), against the 12th 'Slavonia' Division and 'Kalnik' Partisan Detachment of Josip Broz Tito’s partisan forces in the Kalnik mountain region between Varazdin and Krizevci in the puppet state of Croatia in Axis-occupied Yugoslavia (8/25 July 1943).
At the end of June 1943, the 12th 'Slavonia' Division had received orders from the I 'Slavonia' Corps to advance from area of Voćin near Daruvar to the Kalnik mountain region in north-western Croatia with the object of liberating some 200 political prisoners being held in Lepoglava, and also opening the way for the defection of a Croat army artillery battalion in Jalkovec under the command of Major Demetar Varda.
This Yugoslav undertaking compelled the Germans to halt and cancel 'Ivan' and move troops in an unsuccessful attempt to halt the Yugoslav advance. The Axis partners put some 4,000 men into the field for this undertaking, the German contribution being the 462nd Reserve-Grenadierregiment and the 1st Kompanie/202nd Panzerabteilung, and the Croat element comprising the Combat Group 'Peričić' of Pukovnik Stjepan Peričić's 1st Division, 3/2nd Regiment, and six or seven Ustase companies and 12 light tanks of Ustase Pukovnik Ante Moskov’s Poglavnik Bodyguard Brigade.
On 14 July 1943 Germans began their main assault on the 12th and 16th Brigades of the 12th 'Slavonia' Division and the 'Kalnik' Partisan Detachment. The Germans gained the upper hand during the morning and, with armour and air support, made some progress. But in the afternoon the 12th Brigade captured the Ustase garrison in Trakosćan as it advanced toward Slovenia. Hampered in mobility terms, the 12th Brigade fired its last 24 shells into German-held territory and then destroyed the 100-mm (3.94-in) howitzer it had taken in Jelkovac.
On the following day the 12th Brigade continued to fight elements of Generalleutnant Josef Brauner von Haydringen’s 187th Reserve-Division supported by 20 tanks and seven aircraft. As it continued its retreat on 16 July, the 12th Brigade attacked the coal mines at Novi Golubavac and Radoboj, capturing 50 men, destroying installations and burning the mines.
The heaviest combat took place on 20 July, the 12th Brigade suffering 150 casualties including 40 killed. By 21.00 on 20 July the Axis forces completed their encirclement of the 12th Brigade, which was contained on the southern slopes of Kalnik mountain and cut off from the 12th 'Slavonia' Division and the headquarters of the 2nd Operational Zone. The partisans spent most of the night in failed attempts to break out until a time early in the morning when, in the area near Carevdara, the German armour pulled out, leaving only dug-in infantry. This allowed the 12th Brigade to break through, but a rapid German armoured riposte managed to cut off the brigade’s rearguard battalion, which escaped to the north only two days later.
While a quick German reaction and pursuit managed to halt the partisan advance and inflicted significant losses, the defection of the artillery battalion and the liberation of the prisoners at Lepoglava was a major political victory for the partisan movement. After two weeks of sporadic fighting, the partisans withdrew to the south-east from the Kalnik mountain region into the Bilo mountain region.
The Germans admitted the loss of six Germans killed and 20 wounded, and 40 Croats 40 killed, 61 wounded and 66 missing, and claimed 2,350 partisans counted dead and 84 taken prisoner. There was so much fighting going on in the area to the north-east of Zagreb during July 1943 that it is difficult to break it down and determine exactly to what the figure of 2,350 applies. There are no references to massacres, so it probably refers to combined German and Croat claims for the entire area to the north-east of Zagreb between 8 and 25 July, and not just those in the Kalnik mountain region.