'Otto' (iv) was a German and Croat operation against the partisan forces of Josip Broz Tito in the puppet state of Croatia in Axis-occupied Yugoslavia (19/21 April 1943).

The objective of this undertaking was the destruction of the partisans of the 4^th Assault Division operating out of the Grmeč mountains into the Una-Sana bend area of western Bosnia to the south-west of the line between Bosanski Novi and Prijedor. The partisan force managed to exfiltrate itself through the Axis lines and thus escaped the planned encirclement by elements of Generalleutnant Karl Eglseer’s 114^th Jägerdivision supported by Croat forces including the 1^st, 2^nd, 3^rd and 4^th Battalions of Pukovnik Franjo Gjoić's 3^rd Mountain Brigade, 3^rd Battalion of Pukovnik Arnold Redelstein’s 2^nd Mountain Brigade, and 1 and 2/10^th Regiment.

There was little if any contact between the opposing sides, and no losses were reported.