Case White (Fall Weiss), also known as the Fourth Enemy Offensive (Četvrta neprijateljska ofenziva/ofanziva), was a combined Axis strategic offensive launched against the Yugoslav Partisans throughout occupied Yugoslavia during World War II. It was one of the most significant confrontations of World War II in Yugoslavia. The offensive took place in early 1943, between 20 January and mid-to-late March. The Axis operation prompted the Partisan Supreme Command to enact its plans to drive toward eastern Herzegovina, Sandžak and Montenegro.
In order to do this, Tito formed the so-called Main Operational Group, which eventually succeeded in forcing its way across the Neretva in mid-March 1943, after a series of battles with various hostile formations. Other Partisan formations, the 1st Croatian and 1st Bosnian Corps, managed to evade Axis blows and, despite significant losses, reclaim most of the territory they had held before the beginning of the operation.
Since its final stage took place on the Neretva River, the operation was known in Yugoslavia as the Battle of the Neretva (Bitka na Neretvi). This stage is also known as the Battle for the Wounded (Bitka za ranjenike).
In late 1942, with the Axis situation in North Africa deteriorating, the German high command became concerned about the possibility of an Allied landing in the Balkans. In such an event, resistance forces in Yugoslavia would be likely to interfere with German defensive operations as well as their economic exploitation of natural resources, including timber, copper and bauxite. As a result, on 16 December 1942 Adolf Hitler ordered the Armed Forces Commander in Southeast Europe, Generaloberst Alexander Löhr, to crush the resistance in Yugoslavia. In a meeting of 18–19 December, the General Staff of the Wehrmacht decided on the destruction of the Bihać Republic. On 8 January Löhr and Mario Roatta, commander of the 2nd Italian Army, met in Zagreb and devised a detailed plan.
The operation was planned to be carried out in three stages:
Weiss 1 aimed at destroying Partisan-held areas Lika, Kordun, Banija, Cazinska Krajina and Grmeč.