This was a Croat attempt to clear the partisan forces of Josip Broz Tito from the Axis lines of communication, most especially the railway line connecting Doboj and Sarajevo via Maglaj, in Axis-occupied Yugoslavia (3/12 December 1941).
The operation was ordered on 2 November 1941 by the chief-of-staff of the Croat home defence army with the object of destroying the partisan concentrations along the Bosna and Spreča river valleys in eastern Bosnia and in the Ozren mountain area that lie between them, and so preventing the continued sabotage of the rail lines between Maglaj and Doboj and between Tuzla and Doboj.
The formations allocated were General Pješastva Djuro Iser’s II Domobran Corps and General Pješastva Mihailo Lukić’s III Domobran Corps, and at the same time Iser was instructed to plan an offensive against the partisan forces in the Ozren region as Axis trains were being destroyed in this area on an almost daily basis.
With forces from Doboj and an initial arrival of reinforcements, Iser attempted on 15 November to capture, as an essential first move, the most critical single point, which was the village of Lilac situated in the triangle formed by the Bosna and Spreča rivers and the line of communications linking Tuzla and Doboj, and Maglaj and Doboj. After two days of bitter combat, the Croat troops were driven off.
The whole of the ‘Ozren’ (i) undertaking was intended to last three days, and the Croat forces involved were based on Pukovnik Artur Gustović’s 4th Division, totalling some 6,580 men in 16 battalions with the support of four to five battalions of Ustaše troops, between 60 and 70 pieces of artillery, several tanks, three armoured trains, and a small air detachment. The partisan force involved in 'Ozren' (i) totalled about 1,000 personnel in four battalions.
The main part of the offensive began on 2 December, and lasted for nine days before the Croat forces were forced to go over to the defensive after capturing from the partisans only Lipacka glavica and Bajica kamen near Trbuka. During the fighting the partisans managed to capture one mountain gun, one heavy machine gun, 18 light machine guns and more than 200 rifles from the Croat forces, which lost more than 350 men killed and wounded. The partisans lost about 120 dead and wounded.