|Part of World War II in Yugoslavia|
|Commanders and leaders|
|c. 75,000 troops||c. 12,000 troops|
|Casualties and losses|
|c. 6,700 casualties||c. 11,000 partisans killed in operation|
Operation Kugelblitz ("ball lightning") was a major anti-Partisan offensive orchestrated by German forces in December 1943 during World War II in Yugoslavia. The Germans attacked Josip Broz Tito's Partisan forces in the eastern parts of the Independent State of Croatia in an attempt to encircle and destroy them, thereby preventing the Partisans from entering the Territory of the Military Commander in Serbia. Operation Kugelblitz was followed up immediately by Operation Schneesturm (Blizzard) which sought to capitalise on the initial success of Operation Kugelblitz. Both operations are associated with the Sixth Enemy Offensive (Serbo-Croatian: Šesta neprijateljska ofenziva/ofanziva) in Yugoslav historiography.
Operation Kugelblitz, the first of the two offensives, was executed by the 5th SS Mountain Corps. The aim of this operation was to dismantle and consequently destroy Partisan units in eastern Bosnia. The operation ultimately was unsuccessful because the German forces were unable to completely destroy all the Partisan troops. Because of the terrain, large area, and lack of Axis manpower to adequately cover the encirclement, Partisan forces evaded complete destruction by slipping through large gaps in the narrowing encirclement. However, the Partisans still suffered severe casualties.
Operation Schneesturm was initiated immediately upon the completion of Operation Kugelblitz. This operation included twin drives from the Bosnia area. One drive headed westwards towards the Adriatic Sea. The other headed to the northwest and towards the border with Italy. While this operation ended late in December and the Partisans once again survived, the cost was high. The Partisans suffered about 2,000 additional casualties. Although badly battered, the majority of the Partisan units retained their cohesion. Tito's army, in the opinion of some, could still be considered an effective fighting force.
Such in general outline was the sixth offensive on liberated territory in Yugoslavia. The fact that British observers were by this time plentiful on the ground meant that the fighting was adequately reported abroad—as it had never been before—and the conclusion of the campaign coincided with a great wave of publicity for the partisans in England and the United States.
For the Germans their sixth offensive was entirely inconclusive. They had failed to do more than merely interrupt the free development of the resistance movement, and although they burnt large numbers of villages and killed whomever they laid hands on they scarcely reduced the numbers of those who were fighting, and they laid the basis, indeed, for a great increase in those numbers. No reliable estimates of partisan casualties are available; and similarly it is impossible to do more than guess at German casualties. The only statement that can be made without fear of contradiction is that the ratio was heavily in favour of the partisans.