'Grün' (iv) was a German and Croat pair of operations ('Grün I' and 'Grün II') against the partisan forces of Josip Broz Tito in Axis-occupied Yugoslavia (27 February/3 March 1943).
'Grün I' was undertaken in the puppet state of Croatia, and 'Grün II' along the Kupa river between the Sava river and the Farkasic-Kravarsko line.
As part of a larger Yugoslav plan to reduce the pressure on Tito’s main partisan force, the newly formed partisan 18th Independent Brigade, together with the 2nd 'Dilj' Partisan Detachment, carried out 11 actions which destroyed some smaller Axis garrisons and and destroyed railways, forcing the German and Croat military to launch the 'Weiss I' operation to clear the Dilj region. However, the security of the Axis operation was broken and the Central Committee of the Croat communist party in Brod received details of the plan via its contacts in the staff of the Croat II Corps and passed these to the 18th Brigade. This unit was low on ammunition and outnumbered some 10/1, and therefore decided to withdraw to the Krndija mountain.
Taking place between 27 February and 3 March, 'Grün I' had as its objective the engagement and destruction of partisan concentrations (the 18th Brigade of the 4th 'Slavonia' Division and 2nd Partisan Detachment of the 3rd Operations Zone) in the Krndija and Dilj mountain region bordered by Podgorač, Nasice, Čaglin and Levanjska Varos. The German contribution to the operation was centred on the 2/741st Grenadierregiment of Generalleutnant Josef Reichert’s (from 20 February Generalleutnant Karl Eglseer’s) 714th Division, but also included other units as the Gruppe 'Ost' under the command of Pukovnik Andrija Grum, while that of the Croats comprised the 1, 2 and 3/4th Regiment, 3/6th Regiment, 2nd Assault Battalion, 1/Air Force School Regiment, 3rd Battery/4th Artillery Group, 1st and 3rd Batteries/5th Artillery Group, half of the 4th Engineer Battalion, 2nd Signals Battalion, 2/1st Recruit Regiment, most of 15th Ustase Battalion, 1st Company/25th Ustase Battalion, and one company of the 39th Ustase Battalion.
The Croat forces were divided into the Gruppe 'Süd' under Bojnik Rajković, Gruppe 'Ost' under Pukovnik Grum, and the larger Gruppe 'Nordwest' under General Kraus.
The 10,000-man Axis attack began in the Dilj mountain region to the north of Slavonski Brod, but the partisans quickly withdrew to the north-east into the Krndija mountain region just to the south of Nasice. There had been only one skirmish during the operation, near the village of Podgorje, in which the Axis force captured just two animal-drawn wagons. On 5 March, two days after the operation concluded, elements of the 18th Brigade came out of the Krndija mountain region and attacked the Croat garrison in Ljeskovici near Nasice, and captured 61 Croat soldiers. No other details have been found for 'Grün I', which is believed not to have been successful as there were few if any casualties.