'Maibaum' was a German and Croat operation against the partisan forces of Marshal Josip Broz Tito near Vlasenica in the Bosnia region of German-occupied Yugoslavia (24 April/18 May 1944).

Supported by two battalions of Pukovnik Julije Fritz’s 3^rd Jäger Brigade of the Croat home army and several Ustase militia elements, this was a joint undertaking by SS-Brigadeführer und Generalmajor der Waffen-SS Karl Reichsritter von Oberkamp’s 7^th SS Gebirgsdivision 'Prinz Eugen' and SS-Brigadeführer und Generalmajor der Waffen-SS Karl-Gustav Sauberzweig’s 13^th SS Gebirgsdivision 'Handschar' (kroatischs Nr 1), now part of SS-Obergruppenführer und General der Waffen-SS Artur Phleps’s V SS Gebirgskorps, to encompass the destruction of the 16^th 'Vojvodina', 17^th 'East Bosnia' and 36^th 'Vojvodina' Divisions of the Yugoslav III Assault Corps.

On 21 April the III Assault Corps was ordered to move from the Vlasenica area of eastern Bosnia, cross the Drina river, and advance into western Serbia to facilitate the movement of two partisan divisions from the Ibar river valley to the mountain area south-west of Valjevo in western Serbia. The partisans' increasing use of radio communications had allowed German intelligence to break the partisan codes and discover their plans, allowing the German commanders to launch attacks against potential threats.

On 26 April the combined German and Croat force attacked the partisan concentration, broke and dispersed the 36^th Assault Division and blocked the partisan attempt to cross into western Serbia. Heavy fighting continued until 11 May, when the partisans abandoned their plan and the two divisions of the III Assault Corps were ordered to the area of Tuzla and Olovo in eastern Bosnia and told to continue the fight there.

Although no after-action report with a full listing of losses has been found for 'Maibaum', the 7^th Gebirgsdivision claimed the following just on its own account: 2,844 counted partisan dead, many more estimated dead, 1,434 wounded, 1,339 captured and 128 partisan deserters; the division gave no figures for its own losses.

The Yugoslav partisan effort had grown enormously by 1944, and comprised the equivalent of 26 divisions, some of them well equipped, in the bitter struggle with the forces of Generalfeldmarschall Maximilian Reichsfreiherr von Weichs’s Heeresgruppe 'F', which provided the only protection to the four corps of Generaloberst Alexander Löhr’s Heeresgruppe 'E' in the southern part of the Balkans. Formed on 23 August, Heeresgruppe 'E' had 10 divisions (three of them serving as garrison forces on Greek islands) and six fortress brigades comprising some 300,000 soldiers, 33,000 sailors and 12,000 airmen. At the end of the month the defection of Romania to the Soviet camp unseamed the German position in the eastern Balkans, and Heeresgruppe 'E' was ordered to fall back from Greece to a line between Scutari on the Adriatic coast and the Iron Gates pass between southern Romania and Yugoslavia.

For lack of adequate transport the garrisons on Crete and Mílos were abandoned under the command of Generalmajor Georg Benthack, commanding the 133^rd Festungsdivision on Crete, and so too were those of Rhodes, Scarpanto, Kos, Piskopi (Tilos) and Léros under the command of General Wagner. General Helmuth Felmy’s LXVIII Corps pulled out of southern Greece, General Hubert Lanz’s XXII Gebirgskorps fell back from Epiros, General Werner von Erdmannsdorff’s LXXXXI Corps retreated from Thrace, and General Ernst von Leyser’s XXI Gebirgskorps evacuated Albania, all heading to the north through southern Yugoslavia toward the plain of the Sava river. The Yugoslav partisans were very active in trying to hamper this retreat so that Marshal Sovetskogo Soyuza Fyedor I. Tolbukhin’s 3^rd Ukrainian Front could cut them off as it swept from Romania and Bulgaria into Yugoslavia, but the Germans were able to fight their way through before the trap closed.

The Yugoslav partisans were able to liberate Cattaro (Kotor), Ragusa (Dubrovnik) and Spalato (Split), and to take Zara (Zadar), so that at the end of 1944 they controlled all of southern Yugoslavia as well as five large areas (three around Sarajevo and two between Zagreb and Fiume) in German-held northern Yugoslavia.