Operation Southeast Croatia Operation Southeast Croatia ( ) was a large - scale German - led counter - insurgency operation conducted in the southeastern parts of the Independent State of Croatia ( , NDH ) , in modern - day Bosnia and Herzegovina during World War II . It was the first of two German - led operations targeting mainly Yugoslav Partisans in eastern Bosnia between 15 January and 4 February 1942 . Several days after the conclusion of Operation Southeast Croatia , a follow - up operation known as Operation Ozren was carried out between the Bosna and Spreča rivers . Both operations also involved Croatian Home Guard troops and are associated with what is known as the Second Enemy Offensive ( ) in Yugoslav history . The insurgents in the area of operations included some groups led by communists and some led by Serb – chauvinist Chetniks . Although the Partisans and Chetniks had already irrevocably split in the Territory of the Military Commander in Serbia following Operation Uzice , this had not yet happened in eastern Bosnia and in some areas they were still cooperating . As a result , differentiating between the rank and file of the two groups was difficult , as even the communist - led insurgent groups consisted mainly of Serb peasants who had little understanding of the political aims of their leaders . While there were 20 , 000 Chetnik - led insurgents located within the area of operations , they offered no resistance to the German – NDH forces and many withdrew east across the Drina river to avoid being engaged . This contributed to the complete unravelling of Chetnik – Partisan cooperation in eastern Bosnia . The Partisan main force was able to evade the Germans , infiltrate through the Italian cordon to the south and establish itself around Foča . The failure of the Germans to decisively engage the Partisans during these operations necessitated a further major offensive , Operation Trio , in the area immediately south of where Operations Southeast Croatia and Ozren had taken place . Background . On 6 April 1941 the Axis powers invaded Yugoslavia from multiple directions , rapidly overwhelming the under - prepared Royal Yugoslav Army which capitulated 11 days later . In the aftermath of the invasion Yugoslavia was partitioned between the Axis powers through a combination of annexations and occupation zones . Outside of these areas , an Axis puppet state known as the Independent State of Croatia ( NDH ) was established on the territory of modern - day Croatia and Bosnia and Herzegovina . The NDH was divided by a German – Italian demarcation line , known as the " Vienna Line " , with the Germans occupying the north and northeastern parts of the NDH , and the Italians the south and southwestern sections . The NDH immediately implemented genocidal policies against the Serb , Jewish and Roma population . Armed resistance to the occupation and the NDH initially formed into two loosely - cooperating factions , the Partisans who were led by communists , and the Chetniks who were mostly led by Serb – chauvinist officers of the defeated Yugoslav Army . In November and December 1941 , almost all Partisan forces from the Territory of the Military Commander in Serbia had been forced to withdraw into eastern Bosnia where they combined with local Partisan forces . Most of the Chetnik forces in eastern Bosnia were local Serb peasants . The insurgency in eastern Bosnia meant that NDH authorities were unable to retain control of the region . At the end of 1941 , there were six Partisan detachments in eastern Bosnia , with about 7 , 300 fighters operating in the Majevica , Ozren , Birač , Romanija , Zvijezda and Kalinovik areas . According to Enver Redžić , in early January 1942 , the Chetniks controlled a large portion of eastern Bosnia , including the towns of Zvornik , Višegrad , Vlasenica , Srebrenica , Drinjača , Bratunac , Foča , Ustikolina , Goražde and Čajniče . Due to continuing cooperation between the two groups , the Chetniks also shared control of the towns of Rogatica , Olovo and Han Pijesak with the Partisans . Planning . The orders from " General der Artillerie " ( Lieutenant General ) Paul Bader , the German Military Commander in Serbia , directed that Operation Southeast Croatia was to be an encirclement operation . All persons encountered within the area of operations were to be treated as the enemy . The population within the area to be targeted by the operation were almost all either Orthodox Serbs or Bosnian Muslims , although there was a small Catholic Croat minority . Bader believed that the Partisans and Chetniks were using the area as winter quarters , and that their presence there was a threat to major transport routes through eastern Bosnia . The operation itself was led by the German 342nd Infantry Division , which had been relieved of its occupation duties in the Territory of the Military Commander in Serbia by Bulgarian troops . The commander of the 342nd Infantry Division , " Generalmajor " ( Brigadier ) Paul Hoffman , also had the 718th Infantry Division of " Generalmajor " Johann Fortner under his command for the duration of the operation . The German force was assisted by Croatian Home Guard units including seven infantry battalion s and nine artillery batteries . The Axis forces available for the operation were 30 , 000 – 35 , 000 troops in total . Luftwaffe support included reconnaissance aircraft and a combat squadron . The offensive targeted areas held by the Romanija , Zvijezda , Birač , and Ozren Partisan detachments , between Sarajevo , Tuzla , Zvornik and Višegrad . To the south , along the " Vienna Line " separating the German - occupied zone of the NDH from the Italian - occupied zone , the Italians placed a cordon . In total , the area targeted by the operation was estimated by the Germans to contain around 8 , 000 Partisans and 20 , 000 Bosnian Chetniks . The 738th Regiment of the 718th Infantry Division was reinforced by pioneers , four NDH battalions , four NDH artillery batteries and two - and - a - half German mountain gun batteries . It drove east from Sarajevo along the Prača valley towards Rogatica . The other regiment of the 718th Infantry Division , the 750th Regiment , was reinforced by a German artillery battery , an NDH infantry battalion and an NDH mountain battery . It moved south from an assembly area southwest of Tuzla towards Olovo . On 9 January 1942 , the 718th Infantry Division issued orders to both its regiments that defined the following groups as hostile : all non - residents and residents that had been absent from their localities until recently ; all identifiable Chetniks or communists with or without weapons or ammunition ; and anyone concealing , supplying or providing information to those groups . Any captured Partisans were to be briefly interrogated and summarily shot , as were any other insurgents that had attacked the Germans , been caught carrying ammunition or messages , or who resisted or fled . Also , any houses from which shots were fired at German troops were to be burned . This operation commenced on 15 January 1942 . When the Chetnik leaders appointed by Draža Mihailović , Majors Boško Todorović and Jezdimir Dangić , became aware of the commencement of Operation Southeast Croatia , they advised other Chetnik commanders that the operation was targeted at the Partisans , and there was no need for the Chetniks to get involved . Following this , their units withdrew from their positions on the front line , let the Germans pass through their areas , or went home . Many withdrew across the Drina river into the Territory of the Military Commander in Serbia to avoid being engaged , which severely weakened the Partisan defences with the result that they suffered significant casualties and lost a great deal of territory . These actions severed any remaining cooperative links that remained between the Chetniks and Partisans in eastern Bosnia . The insurgents in the area of operations destroyed villages to deny supplies and shelter to the Germans who were operating in mountainous terrain with snow up to deep and facing extreme temperatures approaching . The Partisans proved very difficult to pin down , aided by excellent communication and supported by the local populace . During the operation , only one of the four German regiments involved was able to decisively engage the enemy . The Romanija Detachment made up forty percent of all Partisans in eastern Bosnia and bore most of the burden in the operation . On 21 January , Bader dramatically altered his previous orders regarding the treatment of those encountered in the area of operations , directing that those who did not resist and surrendered or merely had weapons in their houses , were to be treated as prisoners of war . It is likely that this change was intended to assist Chetniks in the area of operations to avoid destruction . By the end of January , Bader ' s chief of staff was attempting to negotiate a cooperation agreement with Dangić , and in turn Dangić ordered the 4 , 500 – 10 , 000 Chetniks under his command to avoid the Germans or surrender their weapons immediately if they were unable to do so . After temporarily improving the Partisan defences against the German and NDH forces , the Partisan Supreme Staff and the 1st Proletarian Brigade were unable to salvage the situation and retreated south towards Foča . The 1st Proletarian Brigade , less two battalions that were accompanying the Supreme Staff , crossed the Igman mountain plateau near Sarajevo with temperatures reaching . According to the commander of the 1st Proletarian Brigade , Koča Popović , 172 Partisans suffered severe hypothermic injury and six died . When they approached the German - Italian demarcation line south of Sarajevo , the Partisans were able to infiltrate through the weak Italian cordon . Montenegrin Partisans crossed into the NDH to attack the Chetniks , capturing Foča on 20 January and Goražde on 22 January . The German and NDH forces were successful in recapturing Sokolac , Rogatica , Bratunac , Srebrenica , Vlasenica , Han Pijesak , Olovo , Bosansko Petrovo Selo , and some smaller settlements , and inflicted significant losses on the Partisans . Because the Chetniks failed to assist the Partisans in the battle , the Yugoslav Central Committee ceased all further attempts to cooperate with them and issued a declaration on 22 January to " Bosnians ! Serbs , Muslims , Croats ! " that Chetnik leaders Boško Todorović , Aćim Babić , and others were traitors . It further proclaimed that the Partisans fought alone " all across Bosnia and Herzegovina " and ended with " long live the united people ' s liberation struggle of all the peoples of Bosnia ! " . The Romanija Detachment ' s commander , Slaviša Vajner - Čiča , was killed in combat against the Germans . A member of the Supreme Staff of the Partisans , Svetozar Vukmanović - Tempo , reported that detachment had completely collapsed . However , faced with overly ambitious objectives and atrocious weather , the combined operation failed to destroy the Partisan forces and was called off on 23 January 1942 , with the Germans having suffered casualties of 25 dead , 131 wounded , and one missing , as well as around 300 cases of frostbite . The NDH forces lost 50 soldiers killed or seriously wounded . The Germans captured 855 rifles , 22 machine guns and four artillery pieces , along with livestock and draft animals . The Partisans had lost 531 killed and between 1 , 331 and 1 , 400 captured , in addition to the frostbite casualties suffered by the 1st Proletarian Brigade while crossing Mt . Igman . A total of 168 NDH and 104 Italian troops that had been captured by the Partisans were freed during the operation . The Supreme Staff entered Foča on 25 January and stayed there for three - and - a - half months . Operation Ozren . Operation Ozren ( ) was aimed at clearing an estimated 2 , 000 Partisans from the area between the Bosna and Spreča rivers , and was effectively an extension of Operation Southeast Croatia employing elements of the force used in that operation . The main force used was Fortner ' s 718th Infantry Division reinforced by a regiment of the 342nd Infantry Division , supported by a number of NDH units ( including a battalion of the Ustaše Black Legion ) . The force was also supported by five tank platoons and an armoured train . Around 20 , 000 Axis troops were committed to the operation . It commenced several days after Operation Southeast Croatia ended on 23 January 1942 . The Germans advanced north and west from Kladanj towards a cordon established by ten Croatian Home Guard battalions supported by their own artillery . The Germans believed they had thoroughly sealed off the area , and checked the Croatian cordon every night , but the majority of Partisans were able to evade the cordon and escape by breaking up into small groups and infiltrating through the cordon through seemingly impassable terrain . The Germans also believed that some Partisans merely withdrew into the mountains , concealing their numbers by walking in each other ' s snowprints , in order to return to the valleys when the Axis forces left . The operation concluded on 4 February 1942 . Aftermath . Both operations were hampered by the German need to rely on their Croatian allies as well as the fact that both forces were ill - equipped for operations in mountainous terrain during extreme winter conditions . The Croatian units had proven not to be a useful addition to the operation , as they possessed little in the way of fighting power , had little unit cohesion and suffered from serious supply problems . Operations Southeast Croatia and Ozren were early opportunities for the Germans to learn lessons about the challenges their poorly equipped and often substandard occupation troops faced fighting in the difficult terrain and weather conditions of Bosnia . However , these lessons were to be repeated many more times in the following years as German commanders persisted with their encirclement tactics and unreasonable expectations of what could be achieved in a given time and space . Following the conclusion of Operations Southeast Croatia and Ozren , German and NDH forces conducted Operation Prijedor in northwest Bosnia . The Germans inflicted considerable losses on the Partisans and captured extensive territory and population centres from them ; however , they failed to eliminate them as a military factor and shortly afterwards had to undertake Operation Trio in the region immediately south of the area of operations for Operations Southeast Croatia and Ozren .