'Ostern' (i) was a German and Croat operation against the partisan forces of Marshal Josip Broz in the puppet state of Croatia within Axis-occupied Yugoslavia (15/17 April 1943).

The undertaking’s objective was the engagement and destruction of a 400/500-strong group of the 'Banija' Partisan Detachment, which was derailing and attacking trains and ambushing road traffic, in the area of Sunja 12.5 miles (20 km) to the south-south-east of Sisak. The German contribution to the operation was elements of several formations and units including Generalleutnant Karl Eglseer’s 114^th Jägerdivision, Generalleutnant Josef Brauner von Haydringen’s 187^th Reserve-Division, the 823^rd Landesschützenbataillon, the 924^th Landesschützenbataillon, the 925^th Landesschützenbataillon, and the 206^th Panzerzüg and 209^th Panzerzüg armoured trains, while that of the Croats was elements of Pukovnik Arnold Redelstein’s 2^nd Mountain Brigade, 2/5^th Mountain Brigade, one company of the 17^th Ustase Battalion, and one Ustase company from Čaprag.

The partisans had left the area before the start of the operation, which therefore yielded no useful results. There were no losses on either side.