On the beginning of spring 1942, Axis forces launched a large anti-partisan drive against Tito's forces in Bosnia Herzegovina southeast of Sarajevo. The Partisan leader cunningly moved his army north, away from the main enemy forces. The two large guerilla columns overran Croatian garrisons along the way, gaining weapons, supplies and even recruits. The besieged troops generally quickly surrendered with the exception of the fanatical Ustachi fascist units. One particularly hard nut to crack was the small town of Kupres. The Ustachis of the infamous "Crna Legija" (Black Legion) fortified it with the support of the local population. The place was defended by a garrison which included peasant militia, an artillery battery and even an armored car, with a grand total of 1500 men. The first attacks by local guerilla forces were easily repulsed and the partisans had to send in their elite Proletarian brigades.
