This was a German and Croat two-part undertaking ('Adler I' and 'Adler II') against the partisan forces of Josip Broz Tito on the Dalmatian coast of Axis-occupied Yugoslavia in the area between Karlobag and Zadar, and in the Adriatic islands after the implementation of 'Achse' (ii) (11/26 November 1943 and 13 January 1944).
The twin operations were designed to secure Ugljan island, a useful base area, against its possible seizure by the Allies and its retention by the 'North Dalmatia' Partisan Detachment.
The undertaking had initially been posited, on 20 October, on the use of German forces to secure the east coast of the Adriatic Sea between Rijeka and Zadar, and involved Generalleutnant Karl Eglseer’s 114th Jägerdivision, elements of Generalfeldmarschall Erwin Rommel’s Heeresgruppe 'B' advancing from the Rijeka region, parts of SS-Obergruppenführer und General der Waffen-SS Felix Steiner’s III SS Panzerkorps (germanisch) and the 14th SS Polizeiregiment. This strength was changed to Generalleutnant Eduard Aldrian’s 373rd Division (kroatisch) and the garrison of Gospić to secure the coast from Karlobag to Novi in 'Adler I', and the 114th Jägerdivision and Generalleutnant Johann Mickl’s 392nd Division (kroatisch) to clear Lika and the islands off Zadar in 'Adler II'. At one point the involvement of Generalleutnant Hermann Niehoff’s 371st Division was also considered. Another variant of the basic plan called for the 114th Jägerdivision to advance first to Gospić and Karlobag, and thence to Otočac and Novi to secure the coast.
During October it became clear to the partisan movement that any direct assault on Gospić garrison was becoming daily less feasible as the initial effects of the Italian capitulation dissipated and German reinforcements started to reach the area, so the decision was taken to blockade Gospić, leaving air drops as the only way for the Germans to supply their garrison. At the same time Tito decided to form the I Proletarian Corps for an advance into Serbia, and for this he requested from the command in Croatia that its best formation, the 6th 'Lika' Division, should be diverted from the siege of Gospić and sent to Bosnia. To replace the 6th 'Lika' Division, one division was ordered to move from Slovenia, but 'Wolkenbruch' prevented this, and the 13th Division was ordered to send its units to positions around Peruić and the 19th Division to send one brigade to southern Lika.
The departure of the 6th 'Lika' Division and the arrival of Generalleutnant Albin Nake’s 264th Division made it possible for the 114th Jägerdivision to be used in several operations designed to push back the partisans in this littoral region. In overall terms, therefore, the undertaking’s objective was for the Axis forces to sweep and clear the partisan forces (13th and 19th Divisions and the 'Otočac' Partisan Detachment) from the coastal sector of northern Dalmatia between Gospić and Karlobag and thence north to Senj. The German contribution to the Axis force was the 114th Jägerdivision and the 264th Division, while that of the Croats was Ustae Pukovnik Čiril Čudina’s 4th Ustae Brigade.
Ultimately the lack of adequate resources compelled the Germans to abandon 'Adler I' in favour of two smaller undertakings, namely 'Nibelungenfahrt' and 'Drenica'.
'Adler II' was the second German offensive by Eglseer’s 114th Jägerdivision and Mickl’s 392nd Division (kroatisch) on the Yugoslav partisan forces which had, since the time of Italy’s September 1943 armistice with the Allies, held the Croat coastal region, Lika and Gorski Kotar (13 January 1944). 'Adler II' was planned for implementation late in December 1943, but in fact started only on 13 January 1944 once the 392nd Division had reached the area of Zagreb, Karlovac and Ogulin and started its advance toward Delnice and Senj in order to link with the 114th Jägerdivision arriving from Dalmatia through Lika via Gospic, Otocac and Senj, in the course of which it fought the Yugoslav 13th 'Primorsko-goranska', 19th 'Dalmatia' and 35th 'Lika' Divisions. At the operation’s successful conclusion, the 392nd Division occupied positions along the Dalmatian coast from Novi to Senj and Karlobag.