'Ziethen' (v) was a German and Croat offensive toward Duvno and Livno in German-occupied Yugoslavia against elements of the 1st Proletarian Division, 6th 'Lika' Division, and 9th, 19th, 20th and 26th 'Dalmatia' Divisions of the Yugoslav VIII Corps of Marshal Josip Broz Tito’s partisan forces (4/23 December 1943).
The operation was undertaken primarily by units of Generalleutnant Karl Eglseer’s 114th Jägerdivision and Generalleutnant Josef Kübler’s 118th Jägerdivision, and elements of SS-Obergruppenführer und General der Waffen-SS Artur Phleps’s V SS Gebirgskorps (105th SS Aufklärungsabteilung and 105th SS Panzerabteilung). The German forces were supported by Croat forces including one battalion of Ustase Pukovnik Rafael Boban’s 5th Ustase Brigade, 1st Domobran Volunteer Regiment, elements of the 15th Regiment, and some 300 Četnik auxiliaries.
The Axis forces' main target was probably the partisans' 1st Air Base located in Livno with grass airfields at Livno and Glamoc to receive supplies from Allies in Italy and also to evacuate wounded partisans and rescued Allied airmen.
Operations began as a northern Kampfgruppe advanced from Knin and Sinj, and a southern Kampfgruppe from the area round Posusje. The important towns of Duvno and Livno were retaken on 5 and 6 December respectively. The German after-action report claimed complete success, including the annihilation of two elite partisan formations (1st Proletarian Division and 6th 'Lika' Division) in the area of Jajce and Bugojno, and the infliction of major reverses on the other four divisions in the area along the coast. A number of partisans defected, and a mass grave of 1,200 people executed by the partisans was uncovered in Livno. Finally, the success of the operation led more than 1,000 men to volunteer for the Croat forces.
According to the records of the Germans, they themselves lost 39 men killed and 173 wounded, with no figures quoted for the Croats, while the partisans lost 750 counted dead and an estimated 1,000 further dead and wounded, 50 prisoners and 165 defectors, as well as booty including 65 machine guns, 437 rifles and one truck. The 1st Air Base lost two-thirds of its personnel (23 dead, two missing and 15 captured), together with one light aeroplane and a considerable quantity of airfield equipment.