This was the German major plan for a general withdrawal from the Dalmatian islands and Adriatic coast of occupied Yugoslavia between Senj and Valona to an average depth of 32 miles (50 km) in order to reach the defences of the 'Grüne-Linie' shielding the German western line of withdrawal from the southern part of the Balkans and to provide additional resources with which to stem the Soviet advance from the east (17 October/early November 1944).
Unlike 'Herbstgewitter' (i) of the previous year, which had been planned and executed as an offensive operation, the 'Herbstgewitter' (iv) operation of 1944 was an essentially defensive undertaking, the choice of the codename probably reflecting the German desire to persuade the partisan forces of Marshal Josip Broz Tito, should they learn of it, that the Germans were intending another offensive operation.
With Soviet forces advancing toward occupied Yugoslavia through Romania and Bulgaria, which had both changed sides, General Maximilian de Angelis’s 2nd Panzerarmee in Yugoslavia, as the primary formation of Generalfeldmarschall Maximilian Reichsfreiherr von Weichs’s Heeresgruppe 'F', was ordered to confront and halt the southern flank of the Soviet advance into the Balkans while also continuing its defence of the Adriatic coast. At the end of August and early in September, therefore, Oberst Werner von Hellebrandt’s 92nd Grenadierregiment (mot.) and 1st Jägerregiment 'Brandenburg' of Generalleutnant Friedrich Kühlwein’s (from 16 October Generalmajor Hermann Schulte-Heuthaus’s) Panzergrenadierdivision 'Brandenburg' were transferred from Dalmatia to area around Belgrade to supplement Generalmajor Hubert Lamey’s 118th Jägerdivision.
In order for the 118th Jägerdivision and Generalmajor Alois Windisch’s 264th Division to operate effectively, the Germans established the 'Grüne-Linie' as a defensive line linking Rijeka in the north to Shkodër in the south via Senj, Velebit, Knin, Mostar, Nevesinje, Gacko, the area to the west of Durmitor and Andrijevica. This line would be held by Generalleutnant Johann Mickl’s 392nd Division (kroatische), Generalmajor Hans Gravenstein’s 373rd Division (kroatische) and Generalleutnant Georg Reinicke’s 369th Division (kroatische). During the retirement to this line, all which could not be removed with the retiring troops was to be destroyed, as were all communications, port facilities etc.
For the start of the withdrawal the date of 17 October was chosen, with Dubrovnik to be evacuated by 20 October and ibenik by 1 November. An earlier withdrawal schedule and a proposal during November that the German forces should pull back still farther, to a line linking Rijeka and Vukovar via Bihać, Banja Luka, Bosanski amac and Vinkovci were summarily rejected by Adolf Hitler and the Oberkommando der Wehrmacht. As well as keeping the Yugoslav resource base and room to manoeuvre, there was also a major political factor involved as a large-scale German withdrawal would be serious blow to Ante Pavelić and Ustae regime of the puppet state of Croatia, to which most of the area in question belonged.
Learning of the German plan from intelligence agents, Marshal Josip Broz Tito’s National Liberation Army and Partisan Detachments of Yugoslavia ordered Major General Pavle Ilić's VIII 'Dalmatia' Corps to start preparations for its response to 'Herbstgewitter' (iv) to prevent any real German success and at the same time gain its revenge for several defeats it had suffered in the preceding 12 months. The Yugoslav plan ordained that the German formations and units would come under attack from the front by the 26th 'Dalmatia' Division and the 1st Tank Brigade on Vis island and from the rear by several Yugoslav divisions operating on the mainland.
The German partial withdrawal from Dalmatian islands soon turned into series of defeats in 'Seydlitz' (vii), 'Eisbär' (vi) and 'Kranich'. The partisan landing on Peljeac and subsequent battle in Vukov Klanac destroyed a major part of the 369th Division before it could be withdrawn from Dubrovnik.
The early withdrawal of the 118th Jägerdivision exposed the flank of the 264th Division, a fact which was exploited by the partisan forces during their 'Split Operation' leading to the main Dalmatian city and port of Split falling into Yugoslav hands largely intact.
As it withdrew from ibenik toward Knin, the Kampfgruppe 'Allermann' was almost surrounded and largely destroyed, though it did manage to break out while nonetheless suffering heavy losses as a result of the partisan forces' lack of co-ordination. But in the 'Knin Operation' most of the 264th Division was destroyed and the 373rd Division also suffered heavy losses. With the fall of Knin, the 'Grün-Line' had been breached by the Yugoslav forces.
Kapitän Weygold’s Kommandant der Seeverteidigung Norddalmatien command had some 3,000 men and 2,000 tons of matériel in need of evacuation. The German navy decided that the ports of Zadar and ibenik should not be abandoned but rather held as strongholds, but the army ordered a full withdrawal to the 'Grün-Line' as rapidly as possible in order to free divisions for redeployment to the Syrmian front. To add to the confusion, while the army was under instructions to leave no one and nothing behind, the navy was ordered to defend the major ports to the last man, and was still receiving from Rijeka pieces of artillery for the improvement of Dalmatian coastal batteries as arranged in earlier plans. Thus three invaluable weeks were lost before navy began to withdraw with major army support.
During this period, the German navy carried out several operations, though these were often harassed by partisan artillery batteries on the Dalmatian islands. On 10/11 October 'Dacapo' was a raid on Molat island against vessels of the partisan Navy; on 16/19 October 'Alfine' was evacuation of matériel from Zadar and ibenik to Rijeka; and on 30/31 October 'Ostern' (ii) was the withdrawal of the Kampfgruppe 'Strecker' from Zadar to ibenik. There were several other evacuation missions before the programme ended with 'Wikinger' (iii), which suffered major losses in an encounter with British destroyers carrying out 'Exterminate'.
'Herbstgewitter' (iv) had been intended to free German formations and units for an improved defence against the advance of the Soviet forces from the east, but failed and in the process suffered heavy losses of men and matériel, much of the latter being seized by the partisan forces. Thus the Germans' new front in the east had to be defended by forces considerably smaller than had been planned. The German forces were saved from total defeat in the west of Yugoslavia only by the partisans' lack of experience in the co-ordination of major operations and, most importantly, their lack of the radio equipment which might have allowed better co-ordination.