Operation Unternehmen 25

operation 25

'Unternehmen 25' was the German invasion and conquest of Yugoslavia (6/18 April 1941).

After invading Greece from Albania during October 1940 in 'Emergenza G', the Italian forces had been driven back into Albania, and Adolf Hitler reluctantly recognised the need to support Benito Mussolini’s Italian Fascist state, not only to restore the diminished prestige of the Axis alliance, but also to prevent the UK from the possible gain of European mainland bases from which to bomb the Romanian oilfields at Ploieşti, the most important single source of the commodity without which the German war machine would effectively cease to function.

After reaching agreement with Bulgaria, Hungary and Romania that these three nations would join the Axis alliance, Hitler then put pressure on Yugoslavia to join this Tripartite Pact. Prince Paul Karađorđević, regent for the young King Petar II Karađorđević, yielded to this pressure on 25 March 1941, but the move was very unpopular with the anti-Axis Serb public and military, and a British-supported coup d'état on 27 March overthrew Prince Paul, the 17-year-old king then taking power with General Dusan Simović as prime minister. Yugoslavia thus effectively withdrew its support for the Axis without formally renouncing the Tripartite Pact, a turn of events which deeply angered Hitler, who was then not placated by a statement from the new Yugoslav government that the country would after all adhere to the Axis did nothing to calm Hitler’s fury. Hitler decided to postpone the 'Barbarossa' attack on the USSR in order to punish Yugoslavia for its defiance, and at the same time conquer Greece and thereby secure the southern flank of the Axis alliance on the mainland of Europe.

On learning of the coup in Yugoslavia, Hitler called his military advisers to Berlin on 27 March, and on the same day issued the Führerweisung Nr 25 ordering that Yugoslavia was henceforward to be treated as a hostile state. Hitler had taken the coup as a personal affront that angered him so deeply that he was determined 'to destroy Yugoslavia militarily and as a state…without waiting for possible declarations of loyalty of the new government'.

On 1 April Yugoslavia redesignated its Assault Command as the Četnik Command, thus recalling the Serb guerrilla forces which had resisted the Central Powers in World War I. This command was to lead a guerrilla war should Yugoslavia be occupied, and its headquarters was transferred from Novi Sad to Kraljevo in south-central Serbia on 1 April.

The ambassador having already been recalled for 'talks', on 2 April the staff remaining at German embassy were ordered to leave the capital and before doing so to warn the embassies of friendly nations to do likewise. Yugoslavia was clearly on the verge of invasion.

Hungary had joined the Tripartite Pact on 20 November 1940, and less than one month later, on 12 December, concluded a treaty with Yugoslavia calling for 'permanent peace and eternal friendship'. The Hungarian leadership was split after the delivery of the Führerweisung Nr 25 on 27 March 1941, however, for while the regent, Vice Admiral Miklós Horthy de Nagybánya, and the Hungarian military establishment favoured a Hungarian involvement in the forthcoming invasion of Yugoslavia and ordered a mobilisation on the following day, the prime minister, Pál Teleki, sought to prevent German troops passing through Hungary and cited the peace treaty with Yugoslavia as an impediment to co-operation with the Germans. On the day of the coup in Belgrade, Hitler had informed the Hungarian ambassador to Germany that events in Yugoslavia might necessitate intervention and that Hungary’s help would in such a case be greatly appreciated. A Hungarian response was thrashed out in council and delivered on 28 March. Two days later, Generalleutnant Friedrich Paulus, the deputy chief of the army general staff, arrived in Budapest and met with Vezérezredes Henrik Werth, chief of the Hungarian general staff, and Altábornagy László Deseő, who proposed that Hungary should mobilise the equivalent of five divisions for the invasion of Yugoslavia: of these, two were to be held in reserve, while Vezérőrnagy Zoltán Decleva’s I Corps, Vezérőrnagy Antal Silley’s V Corps and Vezérőrnagy Béla Miklós’s Mobile Corps were to undertake the main advance on Subotica (Szabadka in Hungarian) as well as a secondary advance in the area to the east of the Tisza river. As a result of the Romanian request that Hungarian troops should not operate in the disputed Banat region, Paulus modified the plan to keep Altábornagy Elemér Gorondy-Novak’s Hungarian 3rd Army in the area to the west of the Tisza river. This final plan was communicated to Berlin and incorporated into operational Order No. 25, issued by Generalfeldmarschall Walther von Brauchitsch, the army’s commander-in-chief, in the course of the same day.

On 3 April, Hitler issued Führerweisung Nr 26 detailing the plan of attack and command structure for the invasion and also promising Hungary territorial gains. On the same day Teleki committed suicide by shooting himself and Horthy, seeking a compromise, informed Hitler that evening that Hungary would abide by the treaty, though it would likely cease to apply should Croatia secede and Yugoslavia cease to exist. Upon the proclamation of an Independent State of Croatia in Zagreb on 10 April, this scenario reached fruition and Hungary joined the invasion, its army crossing into Yugoslavia on the following day.

From north to south round Yugoslavia, between the Istrian peninsula and northern Albania, the Italian forces ranged against Yugoslavia comprised in the north Generale d’Armata Vittorio Ambrosio’s Italian 2a Armata 1 and in the south Generale d’Armata Ugo Cavallero’s Forze Armate 'Albania' 2.

The XIV Corpo d’Armata was supported by one cavalry regiment, three border guard battalions, a finance guard battalion and two Carabinieri (military police) battalions. The XVII Corpo d’Armata included the Gruppo Camicia Nera 'Diamanti' with six Blackshirt regiments each of two battalions, the Albanian-raised Reggimento Camicia Nera 'Skanderbeg' of two battalions, one other two-battalion Blackshirt regiment, one cavalry regiment, one Bersaglieri motorcycle battalion, three border guard battalions, one finance guard battalion, one motorised artillery regiment of three battalions, one military police battalion, and one tank company equipped with M13/40 light tanks. The Settore 'Librazhd' included one motorised artillery regiment of four battalions, one bicycle-mounted Bersaglieri regiment, one cavalry regiment, the Gruppo Camicia Nera 'Biscaccianti' of two Blackshirt regiments with a total of five battalions, the regimental-sized Milizia Foresta Camicia Nera 'Agostini', and the regimental-size Gruppo 'Briscotto' of one Alpini and two finance guard battalions.

The garrison of the Italian Dalmatian coastal enclave of Zara (Zadar) totalled about 9,000 men under the command of Generale di Brigata Emilio Giglioli. This garrison comprised two main groupings and an assortment of supporting units. These main groupings were the regimental-strength Fronte a Terra with three static machine gun battalions and a bicycle-mounted Bersaglieri battalion, and the battalion-strength Fronte a Mare with two machine gun companies, one anti-aircraft battery, one coastal artillery battery and one naval artillery battery. Supporting units consisted of one artillery regiment of three battalions, two independent artillery battalions, one machine gun battalion, one motorised anti-aircraft battalion (less one battery), one engineer battalion, one Camicia Nera company, and one company of L3/35 tankettes.

To support the Italian ground forces, the Italian air force operated from bases in south-eastern Italy, north-eastern Italy and Albania with 658 aircraft, of which 222 were based in Albania with the additional task of supporting the German 'Marita' invasion of Greece. These aircraft comprised 296 fighters, 40 dive-bombers, 192 medium bombers, 12 floatplane bombers and 118 reconnaissance aircraft.

The headquarters of Generale di Squadra Aerea Tullio Toccolini’s 2a Squadra Aerea (2nd Air Force) was located at Padua in north-eastern Italy, and this air force comprised two fighter wings, one bomber wing, two independent bomber groups, three reconnaissance groups and one independent reconnaissance squadron with 90 fighters, 61 medium bombers and 49 reconnaissance aircraft available to support the invasion of Yugoslavia.

The headquarters of Generale di Squadra Aerea Augusto Bonolo’s 4a Squadra Aerea was located at Bari in southern Italy, and the air force comprised two independent fighter groups and one independent fighter squadron, four bomber wings, one combined bomber and naval bomber wing, two independent bomber groups and one independent dive-bomber wing with 73 fighters, 20 dive-bombers, 131 medium bombers and 12 bomber floatplanes.

The headquarters of Generale di Squadra Aerea Ferruccio Ranza’s Comando Aeronautica Albania was located at Tirana in Albania, and this Albanian air command comprised five fighter groups, one dive-bomber group, three independent reconnaissance groups and two independent reconnaissance squadrons with 133 fighters, 20 dive-bombers and 69 reconnaissance aircraft.

Three destroyers of the Italian navy were deployed in the Adriatic in direct support of the invasion, and other units were tasked to deal with the Yugoslav navy.

Operating between the German 2nd Army from Austria and the German 12th Army from Romania and Bulgaria, with the task of advancing from the Szeged area of southern Hungary to the Novi Sad area along the Danube river to the north-west of Belgrade, Gorondy-Novak’s Hungarian 3rd Army comprised Miklós’s Mobile Corps (1st Motorised Brigade, 2nd Motorised Brigade and 1st Cavalry Brigade), Decleva’s I Corps (1st Brigade, 13th Brigade and 15th Brigade), Vezérőrnagy László Horváth’s IV Corps (2nd Brigade, 10th Brigade and 12th Brigade), and Silley’s V Corps (14th Brigade, 19th Brigade and 2nd Cavalry Brigade). A reserve was provided by Vezérőrnagy Gyula Nagy’s VII Corps (9th Brigade, 11th Brigade and 1st Independent Parachute Battalion).

The Hungarian air force provided its 1st Air Brigade to support the Hungarian ground forces. This brigade comprised four fighter groups of the 1st Air Regiment and 2nd Air Regiment flying Fiat CR.42 biplane fighters, one reinforced bomber group from the 3rd Air Regiment and 4th Air Regiment with Junkers Ju 86 and Caproni Ca 135bis twin-engined bombers, and one reconnaissance group of the 5th Air Regiment operating Heinkel He 170A reconnaissance aircraft. Savoia-Marchetti SM.75 transports were used to transport the 1st Parachute Battalion.

Totalling more than 337,000 men and with 875 tanks, 740 other armoured fighting vehicles, 1,500 pieces of artillery, 1,100 anti-tank guns and 2,000 mortars, the German forces comprised Generaloberst Maximilian Reichsfreiherr von Weichs’s 2nd Army 3 assembled in south-western Hungary and south-eastern Austria, and Generalfeldmarschall Wilhelm List’s 12th Army in southern Bulgaria: most of the 12th Army 4 was deployed along the Bulgarian/Greek border in preparation for the 'Marita' invasion of Greece, and of the army’s major formations only the two motorised corps were committed to the invasion of Yugoslavia, though for the first phase of the invasion of Yugoslavia Generaloberst Ewald von Kleist’s 1st Panzergruppe was also assigned to the 12th Army.

At its fully mobilised strength of 1.2 million men, the Yugoslav army could have put 28 infantry divisions, three cavalry divisions and 35 independent regiments into the field. Of the independent regiments, 16 were in frontier fortifications and 19 organised as odred units (combined regiments) each about the size of a reinforced brigade: each odred had one to three infantry regiments and one to three artillery battalions, and three were organised as mountain units. The German attack caught the army in the throes of its belated mobilisation, however, and only some 11 divisions were in their planned defence positions at the start of the Axis invasion, and these formations were at only at something between 70% and 90% of their establishment strengths. As the Yugoslav mobilisation had been slow, tentative and only partial, many divisions were still in the process of mobilisation on 6 April, and the real strength of each Yugoslav army amounted to little more than a corps.

With General Danilo Kalafatović as its chief-of-staff, the Yugoslav army at the time of the Axis invasion comprised, at the organisational level, 29 infantry divisions, three horsed cavalry divisions and one divisional-sized mountain detachment, as well as a large number of independent infantry, cavalry, mountain and combined-arms brigades, infantry and cavalry regiments, fortress troops and 17 border guard battalions. The Yugoslav defence plan located almost all land forces close to the national borders, which meant that there were only very limited strategic reserves held in the country’s interior. The Yugoslav army was reliant largely on animal (mainly ox) transport, and possessed only 50 relatively modern Renault R-35 tanks capable of engaging German armour on qualitative equality, but these were only just being formed into a unit.

The Yugoslav army was organised into the 1st Army Group, 2nd Army Group and 3rd Army Group, the independent 5th Army and 6th Army, and the Coastal Defence Command. The Yugoslav army’s headquarters retained control of five infantry divisions and a large number of smaller infantry, engineer and artillery units, as well as the only operational tank battalion. Each army group and independent army was supported by its own air reconnaissance group attached from the Yugoslav air force.

General Milorad V. Petrović's 1st Army Group comprised General Petar J. Nedeljković's 4th Army deployed behind the Drava river between Varazdin and Slatina with responsibility for the defence of Yugoslav/Hungarian border, and Major General Dusan P. Trifunović's 7th Army responsible for the defence of the north-western border with Italy and Austria. The 4th Army had three infantry divisions, one brigade-strength detachment, one infantry regiment and one cavalry regiment, and it seems that only the 40th Division 'Slavonska' had been partially mobilised and the 27th Division 'Savska' and 42nd Division 'Murska' had only just started to mobilise; the status of the mobilisation of the army’s other elements is unknown. The 7th Army comprised two infantry divisions, two brigade-strength mountain detachments and one brigade-strength detachment, and its seems that the Mountain Detachment 'Triglavski', Mountain Detachment 'Riznajaski' and Detachment 'Lika' had been wholly mobilised, but that the mobilisation of the two infantry divisions had only just been started. The 1st Army Group’s reserve was one cavalry division, who mobilisation was only just starting.

The 4th Army’s support elements included one motorised heavy artillery regiment, one artillery regiment, one motorised anti-aircraft battalion, six border guard battalions, and the 4th Air Reconnaissance Group based at Velika Gorica just to the south of Zagreb. The 7th Army was supported by one artillery regiment and the 6th Air Reconnaissance Group based at Brezice to the north-west of Zagreb.

General Milutin Nedić's 2nd Army Group comprised General Milan M. Rađenković's 1st Army responsible for the area between the Danube and Tisza rivers, General Dragoslav S. Miljković's 2nd Army responsible for the border between Slatina and the Danube river. There was no army group reserve, but the 2nd Army was under orders to create a reserve of one division in the area to the south of Brod. The 1st Army had one infantry division, one cavalry division and three infantry detachments, and the mobilisation of these had started. The 2nd Army had three infantry divisions and one cavalry regiment, and while the mobilisation of the 10th Division 'Bosanska' and 17th Division 'Vrbaska' had been partially completed, that of the third division had only just started and that of the cavalry regiment remains unknown.

The 1st Army was supported by one artillery regiment, one anti-aircraft battalion, and the 1st Air Reconnaissance Group based at Ruma just to the west of Sremska Mitrovica. The 2nd Army was supported by one artillery regiment, one anti-aircraft battalion, one border guard battalion, and the 3rd Air Reconnaissance Group based at Staro Topolje just to the east of Brod.

General Milan Nedić's 3rd Army Group comprised General Ilija D. Brasić's 3rd Army responsible for the defence of the border with Albania between Lake Ohrid to Lake Skadar, and General Jovan M. Naumović's 3rd Territorial Army responsible for the defence of the eastern sector of the Greek border and a sector along the Bulgarian border. The army group reserve comprised the 22nd Division 'Ibarska', which was deployed around Skopje. The 3rd Army comprised four infantry divisions and one cavalry detachment, and while the 31st Division 'Kosovska' (reinforced) and Cavalry Detachment 'Komski' had been completed, that of two other divisions was under way and that of the last division had only just been started. The 3rd Territorial Army comprised three infantry divisions, one infantry detachment and one infantry regiment, and while the mobilisation of the three divisions had been completed, that of the detachment and regiment is unknown, and that of the army group’s reserve, in the form of just one infantry division, had been partially completed.

The 3rd Army’s support units included one artillery regiment, one anti-aircraft battalion, eight border guard battalions, and the 5th Air Reconnaissance Group based at Tetovo to the west of Skopje. The 3rd Territorial Army was supported by one motorised heavy artillery regiment.

General Vladimir J. Cukavac’s 5th Independent Army was responsible for the Romanian and Bulgarian borders between the Iron Gates and the frontier with Greece. The army had four infantry and one cavalry divisions, and while the mobilisation of the 34th Division 'Toplička' and 50th Division 'Drinska' had been completed, that of the 8th Division 'Krajinska' and 2nd Cavalry Division had been partially completed, and that of the last infantry division had only just started. The 5th Independent Army was supported by two motorised heavy artillery regiments, one anti-aircraft battalion, two border guard battalions, and the 2nd Air Reconnaissance Group based at Sarlince to the south of Nis.

General Dimitrije R. Zivković's 6th Independent Army had originally been intended as the Yugoslav army’s strategic reserve, and was deployed around Belgrade and in the Banat region to the east of the Tisza river, but had two infantry divisions in reserve in the lower valley of the Morava river. valley. The army had two infantry divisions, five detachments and two cavalry regiments, and while the mobilisation of the Detachment 'Banatski' had been completed and that of the 49th Division 'Sremska' partially completed, that of the 3rd Division 'Dunavska' had only just been started, and that of the other detachments and regiments is unknown. The 6th Independent Army was supported by one anti-aircraft battalion and the 7th Air Reconnaissance Group based at Smederevska Palanka.

General Zivko M. Stanisaviljević's Coastal Defence Command was responsible for the defence of the Adriatic coast from the Bay of Kotor to Gospić, and comprised one infantry division and four regimental-strength commands, and while the mobilisation of the 12th Division 'Jadranska', the 'Boka Kotorska' Command and 'Sibenik' Command was under way, that of the other two commands is not known. The Coastal Defence Command was supported by one heavy artillery regiment and one anti-aircraft battalion, and a coastal air reconnaissance squadron was based near Mostar.

The Yugoslav army’s general headquarters retained direct command of five infantry divisions, four independent infantry regiments, two motorised engineer regiments and one tank battalion and of another tank battalion which was being crated at the time of the Axis invasion. It also had at its disposal two motorised heavy artillery regiments, 15 artillery battalions, two anti-aircraft battalions and five independent anti-aircraft companies. Of these formations and units, the 1st Division 'Cerska' and 44th Division 'Unska' had been partially mobilised, the 33rd Division 'Lička' and 44th Division 'Unska' had been partially mobilised, and the mobilisation status of the other elements, including the understrength Guards Division, is unknown.

In April 1941, much of the Yugoslav army’s equipment was obsolescent if not actually obsolete, much of it dating from the World War I period. Of the army’s 7,000 pieces of artillery, for example, less than 60% was relatively modern, and only 50 of the tanks on hand were of a quality comparable with Germany’s first-line armour. The army inventory included 1,900 mortars, 800 light anti-tank guns, 823 75-mm (2.95-in) field guns, 180 105-mm (4.13-in) field howitzers, 3,000 howitzers of World War I vintage, 250 anti-aircraft guns, 50 Renault R-35 light tanks, 50 Skoda S-1d light tanks, 50 Renault NC-27 light tanks and 50 Renault FT and M26/27 light tanks.

By April 1941, as a result of its difficulties in sourcing aircraft, the Yugoslav air force was equipped with 11 different types of operational aircraft, 14 types of training aircraft, and five types of auxiliary aircraft. These aircraft used 22 different engines, four different machine guns and two models of aircraft cannon. This made the training, +supply and maintenance of the VVKJ quite problematic. The air force was organised into a headquarters, four air brigades and one naval brigade with more than 423 aircraft of Yugoslav, German, Italian, French, Czechoslovak and British design, in addition to 20 largely civilian transport aircraft which had been pressed into military service. The air force’s primary warplanes were 73 Messerschmitt Bf 109E, 38 Hawker Hurricane Mk I (with more being built under licence in Yugoslavia), 30 Hawker Fury Mk II, eight Ikarus IK-2 and six Rogozarski IK-3 (plus more under construction) fighters, 63 Dornier Do 17K, 60 Bristol Blenheim Mk I and 40 Savoia-Marchetti SM.79K bombers. Of these, 107 of the fighters were of modern design, while the rest were not capable of meeting front-line Axis aircraft on anything approaching equal terms. Some of the bomber and reconnaissance aircraft were also considered obsolete for the same reason.

The naval air arm had eight squadrons equipped, among a number of auxiliary types, with 12 Dornier Do 22K and 15 Rogozarski SIM-XIVH patrol floatplanes.

The Yugoslav navy had one elderly ex-German light cruiser suitable only for training, one large modern destroyer flotilla leader of British design, two modern destroyers of French design, one seaplane tender, four modern submarines and 10 modern motor torpedo boats. There were also six medium torpedo boats inherited from the previous Austria-Hungarian navy, six minelayers, four large armoured river monitors and various auxiliary craft.

On 6 April, the Axis forces attacked Yugoslavia from the north and east.

The Luftwaffe opened the 'Unternehmen 25' campaign with 'Bestrafung', a saturation bombing raid on Belgrade, the Yugoslav capital, in the early morning. Flying in relays from airfields in Austria and Romania, 150 bombers and dive-bombers General Alexander Löhr’s Luftflotte IV, Oberstleutnant Karl Christ’s Fliegerführer 'Graz' and Oberstleutnant Clemens Graf von Schönborn-Wiesentheid’s Fliegerführer 'Arad' commands, escorted by the latter two commands' fighters, carried out this 'terror' effort. The initial raid was carried out by three distinct waves of aircraft, each bombing for 20 minutes and followed after a 15-minute interval by the next wave. The city was thus devastated by a deluge of bombs lasting 90 minutes. The German bomb-aimers directed their main effort against the centre of the city, the location of the main government buildings. The weak Yugoslav air force and completely inadequate anti-aircraft defences were saturated by the German attacks and soon destroyed, which allowed the dive-bombers to come down to very low level before releasing their bombs with increased accuracy. For the loss of just two of their own fighters, the Germans destroyed 20 Yugoslav aircraft in the air and 44 on the ground. When the attack was over, it is possible that more than 17,000 of Belgrade’s inhabitants lay dead under the debris, and all means of communication between the Yugoslav high command and its major formations had been effectively destroyed. Although some elements of the general staff managed to escape to one of the suburbs, the co-ordination and control of operations in the field were rendered impossible from the outset.

With the heart of Yugoslavia’s governmental, administrative and military capability thus crippled, General Wolfram Freiherr von Richthofen’s VIII Fliegerkorps, operating from bases in western Bulgaria, was able to devote its potent and highly experienced air units to the tactical destruction of the Yugoslav army even as it was still in the early stages of its mobilisation, airfields and lines of communication, and also to the close support of the German ground forces.

The Luftwaffe’s devastating air assault on Belgrade was paralleled by the initial thrust of the XL Corps (mot.) from Bulgaria towards Skopje. On 8 April there followed the assault of the XIV Corps (mot.) from Bulgaria towards Nis, and on 10 April four more thrusts struck the Yugoslav army: these were advances of the XLI Corps (mot.) from Romania toward Belgrade, of the XLVI Corps (mot.) from Hungary across the Drava river, of the LI Corps from Austria toward Zagreb, and of the XLIX Gebirgskorps from Austria toward Celje. By the end of 10 April the Yugoslav army was already disintegrating, with formations and units right across the country either retreating or surrendering: the one exception was the forces on the Albanian frontier.

Italy and Hungary joined the ground offensive on 11 April. The Italian part in the ground offensive began as its 2nd Army attacked from north-eastern Italy towards Ljubljana and to the south-east along the Dalmatian coast, encountering almost no resistance in the process. On the same day, the Hungarian 3rd Army crossed into Yugoslavia and advanced toward Novi Sad. Neither the Italian nor the Hungarian armies met serious resistance. On 12 April, German troops captured Belgrade and Ljubljana fell to the Italians. On 14/15 April, King Petar and the government flew out of Yugoslavia, and the Yugoslav supreme command was captured by the Germans near Sarajevo. The Yugoslav surrender was signed on 17 April.

After the coup on 25 March, the Yugoslav armed forces had been put on alert, though no order for the full mobilisation had been issued in the hope of placating Hitler. The air force had decided to disperse its forces from their main bases to a system of 50 pre-prepared auxiliary airfields, but many of these lacked facilities and were characterised by inadequate drainage, which prevented the continued operation of all but the very lightest aircraft in the adverse weather conditions prevailing in April. Despite having a strength which was notionally greater in terms of its modern warplanes than the combined British and Greek air forces to the south, the Yugoslav air force was wholly incapable of matching the overwhelming German and Italian air superiority in terms of numbers, tactical deployment and combat experience.

Luftflotte IV committed a strength of seven Kampfgruppen to the campaign in the Balkans and , as noted above, its first effort, ordered directly by Hitler, was the 'Strafgericht' bombing of Belgrade. The medium bomber Kampfgruppen continued their attack on t’he city of Belgrade for several days, while the Stuka dive-bomber wings were soon diverted to attacks on Yugoslav airfields. With its knock-out blow delivered on the centre of the Yugoslav administrative and communications centre, therefore, the Luftwaffe was able to concentrate its efforts against purely military targets such as Yugoslav airfields, routes of communication, and troop concentrations, and also to the close support of the German ground operations.

For the defence of Belgrade, the Yugoslav air force had deployed the six squadrons of the 32nd and 51st Fighter Groups to attack each wave of bombers, although as the day continued the four squadrons of the 31st and 52nd Fighter Groups, based in central Serbia, also became involved. The Bf 109E, Hurricane Mk I and IK-3 fighters scored at least 20 victories over the attacking bombers and their escorting fighters on 6 April, and another 12 on 7 April. Its desperate and ultimately fruitless defensive effort over Belgrade cost the Yugoslav air force some 20 fighters shot down and 15 damaged.

The Yugoslav bomber and maritime force attacked targets in Italy, Austria, Hungary, Romania, Bulgaria and Albania, and also attacked German, Italian and Hungarian troops. Meanwhile, the fighter squadrons inflicted not insignificant losses on escorted German bomber raids on Belgrade and other targets in Serbia, as well as on Italian raids on targets in Dalmatia, Bosnia, Herzegovina and Montenegro. The Yugoslav air force also provided direct air support to the Yugoslav army by strafing Axis marching troops and mechanised columns in Croatia, Bosnia and Serbia, on occasion taking off and strafing the troops attacking the base from which they had take off even as it was being evacuated.

After a combination of air combat losses, losses on the ground to Axis air attacks on its bases and the overrunning of its airfields by Axis troops, after 11 days the Yugoslav air force had almost ceased to exist. However, continued domestic production during 'Unternehmen 25' supplied the Yugoslav air force with an additional eight Hurricane Mk I, six Do 17K, four Blenheim Mk I, two IK-2, one IK-3 and one Bf 109 from the local aeronautical industry’s aircraft factories and workshops.

On 6 April, Luftwaffe dive-bombers and ground-attack fighters destroyed 26 of the Yugoslav Do 17K bombers in the initial assault on their airfields, but the remaining aircraft were able to strike back with a number of attacks on German mechanised columns and Bulgarian airfields. By the end of the campaign total Yugoslav losses stood at four Do 17K bombers destroyed in air combat and 45 destroyed on the ground. On 14/15 April, the last seven Do 17K machines flew to Niksić airfield in Montenegro and took part in the evacuation of King Petar, members of the Yugoslav government and the Yugoslav gold reserves to Greece; also involved were SM.79K and Lockheed Electra aircraft. After the completion of their mission, five Do 17K machines were destroyed on the ground when Italian aircraft attacked the Greek-held Paramitia airfield. Only two Do 17K aircraft escaped destruction in Greece and later flew across the Mediterranean Sea to join the British air strength in Egypt. In all, 18 bomber, transport and maritime patrol aircraft (two Dornier Do 17K, four SM.79K, three Electra, eight Dornier Do 22K and one SIM-XIV-H machines) succeeded in escaping to Egypt at the end of the campaign.

At 16.00 on 15 April Löhr, the commander of Luftflotte IV, received an order from Reichsmarschall Hermann Göring, the Luftwaffe’s commander-in-chief, to end the air campaign in Yugoslavia and start the transfer of most of Luftflotte IV's dive-bomber force to support the 'Marita' campaign in Greece.

In an unco-ordinated fashion, the British, Greek and Yugoslav high commands had intended that Nis would be the linchpin of their attempts to wear down the German forces in the Balkans, and it was for this reason that the locality, in the upper reaches of the Morava river, was important to each side. When the Germans broke through in this sector, whose retention was vital to the Yugoslavs if stability was to be maintained on the front, the Yugoslav supreme command committed numerous forces from its strategic reserves, including Major General Dimitrije T. Predić's 2nd Cavalry Division, but these were harassed by the Luftwaffe during transit to the front and did not get through in any significant quantities.

Having reached Nis from its initial attacks from Bulgaria and broken the Yugoslav defences, the XIV Corps (mot.) headed to the north-west in the direction of Belgrade. Farther to the north, the XLVI Corps (mot.) had advanced across the Slavonian plain from Austria to attack Belgrade from the west, while the XLI Corps (mot.) threatened the city from the north after launching its offensive drive from Romania and Hungary. Thus, by 11 April, Yugoslavia was being criss-crossed by German armoured columns, and the only resistance which remained was a large nucleus of the Yugoslav army around the capital, and after a day of heavy fighting German armoured forces broke through these Yugoslav defences and occupied Belgrade during the night of 12/13 April.

On 10 April, the Independent State of Croatia was established in Zagreb by the Ustase, and on the same day Horthy and the new Hungarian prime minister, László Bárdossy, issued a joint declaration that Yugoslavia had ceased to exist, releasing Hungary from its obligations under the non-aggression pact and the Treaty of Trianon. According to the declaration Hungarian troops would now act to protect Hungarians living in what had been north-eastern Yugoslavia from the anarchy beginning to sweep the area. On the following day the Hungarian 3rd Army started to occupy those regions of Yugoslavia using one cavalry, two motorised and six infantry brigades of the the Mobile Corps, IV Corps and V Corps, with the I Corps and VII Corps still held back in reserve, and the headquarters of the Hungarian 3rd Army informed that of the German 2nd Army that its forces had crossed the frontier to the north of Osijek and near Subotica. The Hungarian 3rd Army faced the Yugoslav 1st Army, and by the time the Hungarians crossed the border, the Germans had been attacking Yugoslavia for over a week. As a result, the Yugoslav forces confronting the Hungarians put up little resistance, the exceptions being the units in the frontier fortifications, which did delay the Hungarian advance for some time.

The speed and depth of the Germans' advances during the initial stage of 'Unternehmen 25' had forced the Yugoslavs to make major tactical withdrawals of their forces facing the Hungarian formations, so there was no significant fighting between the two armies. The Hungarian forces advanced to the south as far as the Danube river between Vukovar and the confluence with the Tisza river without any real military resistance. Serb Četnik irregulars fought isolated engagements, and the Hungarian general staff in fact came to see these irregular resistance forces to be the Hungarians forces' only significant opposition.

On 12 April, part of the the Hungarian 1st Parachute Battalion captured canal bridges at Vrbas and Srbobran. Sombor was taken in the face of determined Četnik resistance, and Subotica was also seized. The first airborne operation in Hungarian history was not lacking in incident. The 'battalion' was delivered in five Italian-made SM.75 transport aircraft formerly on the strength of the civilian airline MALERT but impressed into service with the Hungarian air force in September 1939. Soon after taking off from the airport at Veszprém-Jutas during the afternoon of 12 April, the command aeroplane crashed with the loss of all on board, which including 19 paratroopers, and this was the heaviest single loss suffered by the Hungarians during the Yugoslav campaign.

On 13 April, the 1st Motorised Brigade and 2nd Motorised Brigade occupied Novi Sad and then advanced to the south across the Danube river into the northern part of Croat Syrmia, taking Vinkovci and Vukovar on 18 April. The brigades then drove to the south-east and took the western Serb town of Valjevo one day later. Other Hungarian forces occupied the Yugoslav regions of Prekmurje and Međimurje. The news of the Hungarian military success in Yugoslavia, which had taken the areas which had been part of Hungary before the Treat of Trianon, part of the settlement arrangements following World War I, was welcomed in the Hungarian parliament. German forces occupied a narrow sector of north-eastern Prekmurje along the German/Yugoslav border as this included four Volksdeutsche (ethnic German) villages, and in the middle of June 1941 the area was absorbed into the Reichsgau Steiermark.

Hungarian troops had suffered 126 dead and 241 wounded during the low-intensity fighting, and killed between 1,122 and 3,500 civilians, including some Volksdeutsche, and many other civilians were arrested and tortured. On 14 April some 500 Jews and Serbs were bayoneted to death, probably as a warning to others not to offer any resistance.

The Yugoslav R-41 war plan, formulated before the outbreak of hostilities, stipulated that in the face of a major Axis invasion the Yugoslav forces were to fall back on all fronts except that in the south. Here the Yugoslav 3rd Army, in co-operation with the Greek forces, was to launch an offensive against the Italian forces in Albania. This was designed to secure the area which would make possible the withdrawal of the main Yugoslav forces to the south via Albanian territory in order to reach Greece and join the Allied forces which were to be based there. The strategy was based on the premise that the Yugoslav army would, together with the Greek and British Armies, thus constitute a new version of the Salonika Front of World War I.

On 8 April the hard-pressed Yugoslav air force despatched one squadron of 14 Breguet Bre. 19 light bombers to the city of Florina in northern Greece with the object of providing assistance to both the Yugoslav and Greek armies on the Macedonian front. The squadron undertook many bombing and strafing missions during the course of the campaign.

Part of the 3rd Army Group, the Yugoslav 3rd Army was under instruction to undertake offensive operations against the Italian 9th Army in northern Albania. For this purpose the 3rd Army had concentrated four infantry divisions and one combined regiment (odred) in the Montenegro and Kosovo regions: the Yugoslav formations and units were thus the 15th Division 'Zetska', 13th Division 'Hercegovacka', 31st Division 'Kosovska', 25th Division 'Vardarska' and Cavalry Odred 'Komski'. The 3rd Army Group’s strategic reserve was the 22nd Division 'Ibarska', and this was situated around Urosevac in the Kosovo region. In addition, offensive operations against the Italian enclave of Zara on the Dalmatian coast were to be undertaken by the 12th Division sJadranskas.

The 3rd Army began its offensive into northern Albania on 7 April as the Cavalry Odred sKomskis covering Gusinje-Prokletije mountain area started to advance in the direction of the village of Raja-Puka. The 31st Division crossed the border in the Prizren area of Kosovo and advanced through the Drin river valley. The 25th Division gained some local success at Debar while the rest of the 3rd Army’s formations and units were still assembling.

On 8 April the 15th Division advanced steadily along the road from Podgorica to Shkodër. The Cavalry Odred 'Komski' crossed the difficult Prokletije mountains and reached the village of Koljegcava in the Valjbone river valley. Farther to the south, the 31st Division broke through the Italian defences in the Drin river valley but then, as a result of the fall of Skopje to the Germans, the 25th Division was forced to bring to a halt its operations in Albania.

There was little further Yugoslav progress on 9 April, because although the 15th Division continued its progress toward Shkodër and the Cavalry Odred 'Komski' reached the Drin river, the 31st Division had to halt all combat activities on the Albanian front as German troops appeared in Prizren. On 10 April the 15th Division was still steadily fighting its way towards Shkodër and had advanced as much as 30 miles (50 km) in some places. These advances had been supported by aircraft of the Yugoslav air force’s 66th and 81st Bomber Groups, which attacked airfields and Italian troop concentrations around Shkodër, as well as the port of Durrës. The Cavalry Odred 'Komski' and the right-hand column of the 31st Division advanced along the right bank of the Drin river toward Shkodër in order to link with the 15th Division, but the division’s central and left-hand columns were forced to go onto the defensive to hold off the increasing pressure exerted in their rear by German troops.

Between 11 and 13 April, with German and Italian troops advancing on its rear areas, the 15th Division was forced to retreat to the Pronisat river by the Italian 131a Divisione corazzato, and remained there until the end of the campaign on 16 April. The 131a Divisione corazzato then advanced in the direction of the Yugoslav fleet base of Kotor in Montenegro, also occupying Cettinje and Podgorica.

At the local level, internal nationalist rivalries within Yugoslavia were indicated by the fact that infighting had begun even before the arrival of Axis troops. Croats of the 40th Division’s 108th Regiment mutinied during the evening of 7/8 April near Grubisno Polje, taking command of the regiment from its Serb officers, and were then joined by the 40th Auxiliary Regiment and elements of the 42nd Regiment also of the 40th Division. With the situation in its area deteriorating rapidly, the 4th Army’s headquarters was moved from Bjelovar to Popovača. The mutinous regiments then entered Bjelovar, whose mayor proclaimed an Independent State of Croatia on 8 April. Two senior Croat civilian leaders sent messages to the city urging the regiments to maintain their positions, but these were ignored by the mutinous military and civil officials, who awaited the arrival of German forces.

On 10 April there were clashes in Mostar between Yugoslav troops and Ustase supporters, the latter taking control of the city. Several Yugoslav aircraft were damaged and disabled on Jasenica airfield near Mostar, these including several Do 17s and SM.79K bombers.

On 11 April Ustase agents seized power in Čapljina, and intercepted and disarmed Yugoslav troops moving by rail from Mostar to Trebinje. A Yugoslav back-up force from Bileća was then despatched and retook the town on 14 April, before the arrival of the Germans in the coming days.

As 'Unternehmen 25' started, the Yugoslav navy had available three destroyers, two submarines and 10 motor torpedo boats as the most effective units in its fleet. One other destroyer, Ljubljana, was in dry dock at the time, and her guns were used in defence of the fleet base at Kotor. The remainder of the fleet was useful only for coastal defence and local escort and patrol work. Kotor lies close to the Albanian border and the Italo-Greek front there, but Zara, an Italian enclave, was to the north-west along the coast, and to prevent a more substantial Italian lodgement being established there, the destroyer Beograd, four old torpedo boats and six motor torpedo boats were despatched to Sibenik, 50 miles (80 km) to the south of Zara, in preparation for an attack. This was to be co-ordinated with the land assaults of the 12th Division and two combined-arms odreds attacking from the area of Benkovac area with the support of air attacks by the 81st Bomber Group. The Yugoslav forces launched their attack on 9 April, but by 13 April the Italian forces had counterattacked and were in Benkovac by 14 April. The naval prong to this attack faltered when the destroyer Beograd was damaged by near misses from Italian aircraft off Sibenik, the warship’s starboard engine being rendered inoperative, after which she limped to Kotor, escorted by the remainder of the force, for repair. Maritime patrol floatplanes flew reconnaissance and attack missions during the campaign, as well as providing air cover for mine-laying operations off Zara, and some of their successes included an Italian tanker damaged by a near miss off the Italian coast near Bari, attacks on the Albanian port of Durrës, and attacks on Italian supply convoys to Albania. On 9 April, one Do 22K floatplane notably took on an Italian convoy of 12 ships with an escort of eight destroyers crossing the Adriatic Sea during the day, attacking single-handed in the face of intense anti-aircraft fire.

The Yugoslav navy also included in its strength the four large, heavily armed and armoured river monitors of its riverine flotilla. These were used to patrol the Danube, Drava and Sava rivers in the northern parts of Yugoslavia and its border with Hungary. The monitors were Drava, Sava, Morava and Vardar, which had been inherited from the Austro-Hungarian navy as Yugoslavia came into existence after the end of World War I. Each had a displacement of some 400 to 500 tons and carried a main armament of two 120-mm (4.72-in) guns, two or three 66-mm (2.6-in) guns, 120-mm (4.72-in) mortars, 40-mm anti-aircraft guns and machine guns. At the start of the campaign the monitors undertook offensive operations by shelling the airfield at Mohács in Hungary on 6 April and again two days later, but had to begin withdrawing towards Novi Sad by 11 April after coming under repeated attack by German dive-bombers. Early in the morning of 12 April, a squadron of Ju 87 dive-bombers again attacked the Yugoslav monitors on the Danube river. Drava was hit by several of bombs, which failed to penetrate the monitor’s 25-mm (1-in) deck armour, until, by chance, one bomb fell straight down the funnel, killing 54 of the 67-man crew. During the attack anti-aircraft gunners on the monitors claimed three dive-bombers shot down. The remaining three monitors were scuttled by their crews later on 12 April as German and Hungarian forces had occupied both their bases and the river systems on which they operated.

On land, the Axis formations attacked right round Yugoslavia’s land frontiers. While the Italians in the north and south (the former aided by four of Giglioli’s battalions debouching from the Italian coastal enclave at Zara) concentrated on advances along Yugoslavia’s Dalmatian coast on the Adriatic Sea to meet at Dubrovnik on 17 April, as noted above the Hungarian 3rd Army pinched off the Vojvodina salient of Yugoslav territory extending to the north-east in the direction of Szeged in Hungary.

This left the main weight of the undertaking to the two German armies, which converged on Belgrade from three different directions. Early in the morning of 8 April von Kleist’s 1st Panzergruppe moved to the west from its assembly area to the north-west of Sofia. Crossing the frontier near Pirot, the XIV Corps (mot.), spearheaded by Crüwell’s 11th Panzerdivision followed by Fehn’s 5th Panzerdivision, Gabcke’s 294th Division and Eglseer’s 4th Gebirgsdivision, advanced to the north-west in the direction of Nis on the Morava river. Despite adverse weather, a succession of road blocks, and determined resistance by elements of the 5th Army, the 11th Panzerdivision was effectively supported by powerful artillery and air power, and quickly broke right through the Yugoslav line on this first day. The commander of the 5th Army was so depressed by this major German success, suggesting that his forces lacked the training and equipment to check the German thrust, that he ordered his formations to fall back into the area to the west of the Morava river. This was a move which could not be completed because, as early as 9 April, the leading German armoured units streamed into Nis, cutting off much of the 5th Army on the eastern side of the Morava river.

The German armour then immediately wheeled to the north-west up the western side of the Morava river toward Belgrade over valley terrain decidedly favourable for it. To the south of Paraćin and south-west of Kragujevac, parts of the 5th Army once again attempted to check the 1st Panzergruppe's advance, but were quickly routed after some heavy fighting. The Germans took more than 5,000 Yugoslav prisoners in this one encounter. Meanwhile the 5th Panzerdivision was temporarily stalled by the poor condition of the roads near Pirot and then, when it was on the move once more, was instructed to wheel to the south just below Nis and cut off the Yugoslav forces around Leskovac. When it became apparent that the Nis front was about to collapse, the 5th Panzerdivision reverted to the direct control of 12th Army and joined the XL Corps (mot.) which, with the XVIII Corps, was now concentrating on the 'Marita' campaign against Greece.

On 10 April, meanwhile, the formations of the XIV Corps (mot.) were moving rapidly down the valley of the Morava river in close pursuit of the Yugoslav forces falling back toward Belgrade. On the following day the German spearheads drove into the southern flank of the retreating 6th Army, which they overran during the early hours of 12 April. By the evening of that day the 1st Panzergruppe, with the XI Corps on the right of the XIV Corps (mot.), was less than 40 miles (65 km) to the south-east of Belgrade. The two Yugoslav armies which the 1st Panzergruppe had met were now so disorganised and demoralised that they were in no position even to delay the German thrust or cut the German lines of communications, the latter extending some 125 miles (200 km) from the point at which they entered Yugoslavia to the north-west and south-west of Sofia, the capital of Bulgaria.

Timed to coincide with the drive of the XIV Corps (mot.) from the south-east, the XLI Corps (mot.) had moved to the south-west from its concentration area to the south of Timişoara in Romania across the south-eastern part of the Banat straight toward Belgrade. This attack was spearheaded by the Regiment (mot.) 'Grossdeutschland', followed closely by Hausser’s SS Division (mot.) 'Reich'. After crossing the frontier to the north of Vrsac, the leading German elements reached Pančevo on 11 April. Having advanced to a point some 40 miles (65 km) to the north of Belgrade, the main body of the XLI Corps (mot.) met only isolated resistance on the following day as it swept rapidly south toward the Yugoslav capital.

Farther still to the north, in the sector of the 2nd Army, the primary motorised (and partially armoured) formation was the XLVI Corps (mot.) on the Hungarian side of the Drava river to the south of Lake Balaton’s south-western end. When the Luftwaffe undertook 'Strafgericht' on 6 April, the 2nd Army was still grouping its formations along Yugoslavia’s northern frontiers with Hungary and Austria, in preparation for its advance, scheduled to start on 10 April. In an effort to improve their lines of departure, some of the 2nd Army's formations took advantage of the interim period to launch limited-objective attacks all along the frontier zone. The troop commanders had to keep their forces in check to prevent major engagements from developing prematurely, which might have had an adverse effect on the 2nd Army's freedom of action.

The most important initial objective for the XLVI Corps (mot.) was the seizure of the main bridges in its sector before the Yugoslav forces could demolish them. As early as 1 April, therefore, elements of the XLVI Corps (mot.) had been ordered to take the bridge at Bares and the rail bridge about 10 miles (16 km) to the north-east of Koprivoica by coups-de-main. By a time early in the evening of 6 April, the lack of Yugoslav resistance and the overall situation suggested that the Yugoslav army was not prepared to make a concerted stand along the border, and the XLVI Corps (mot.) was instructed to establish bridgeheads across the Mura and Drava rivers at Mursko Sredisce, Letenye, Zakany and Barcs. The few local attacks carried out by the corps caused dissension in the ranks of the Yugoslav 4th Army, which included a high percentage of Croats desirous of creating and independent Croatia allied with the Axis powers. Croat soldiers mutinied at several points in the Drava salient, refusing to resist the Germans, whom they saw as their liberators from Serb oppression.

When the German forces crossed the Drava bridge at Bares during the morning of 10 April and broke out of the previously established bridgeheads, the opposing Yugoslav 5th Army was already on the verge of disintegration. With the powerful air support characteristic of German land offensives, Brandenberger’s 8th Panzerdivision, followed by Henrici’s 16th Division (mot.), began the offensive of the XLVI Corps (mot.) toward Belgrade by moving south-east between the Drava and Sava rivers. By the evening of 10 April leading elements of the 8th Panzerdivision, having met almost no resistance, had reached Slatina despite poor roads and adverse weather.

After a swift mopping up of pockets of Yugoslav resistance, the division headed in the direction of Belgrade via Osijek, where the roads became even worse. On 11 April the 8th Panzerdivision reached the Osijek region, and behind it the 16th Division (mot.) was advancing beyond Nasice. Both divisions were now delayed by poor roads and blown bridges, slowing the XLVI Corps (mot.) in its task of falling on the rear of the Yugoslav facing the XIV Corps (mot.) advancing from the south-east, and so establishing contact with the 1st Panzergruppe. At 02.30 on 12 April the 8th Panzerdivision entered Mitrovica after two vital bridges across the Sava had been captured intact. The division continued its thrust, the main body moving on Lazarevac, about 20 miles (32 km) to the south of Belgrade, which was the point allocated for the meeting with the 1st Panzergruppe.

During the afternoon of 12 April, however, the XLVI Corps (mot.) received new orders, indicating that only elements of the 8th Panzerdivision should continue their eastward drive to take and hold the Sava river bridge near the western outskirts of Belgrade. At 18.30 the division’s main body wheeled to the south-east in the direction of Valjevo to establish contact with the left wing of the 1st Panzergruppe in the area to the south-west of Belgrade. At the same time the 16th Division (mot.), which had been following the 8th Panzerdivision, turned to the south, crossed the Sava and advanced on Zvornik. Thus both divisions were diverted from their original objective, Belgrade, to become involved in the advance on Sarajevo.

Meanwhile, both the 2nd Army and the Oberkommando des Heeres were waiting to learn that Belgrade had been taken. Of the three converging motorised (partially armoured) formations, the XLI Corps (mot.) was closest to the Yugoslav capital after reaching Pančevo on the eastern bank of the Danube river some 10 miles (16 km) to the east of the city. To the south of Belgrade resistance stiffened as the 11th Panzerdivision, spearheading the 1st Panzergruppe, neared Belgrade. As the three formations were converging on Belgrade simultaneously, the Oberkommando des Heeres was not immediately able to determine which force was the first to reach the Yugoslav capital. In the early evening of 12 April SS-Obersturmführer Fritz Klingenberg of the SS Division 'Reich' (mot.), finding all the Danube river bridges destroyed, took a patrol across the river on captured inflatable rafts. The patrol entered the city unmolested, and at 17.00 hoisted the German flag above the German legation. About two hours later the mayor of Belgrade officially surrendered the city to Klingenberg, who was accompanied by a representative of the German foreign ministry previously interned by the Yugoslavs.

No word from the 8th Panzerdivision's leading elements, last reported approaching the western outskirts of Belgrade, had been received at the headquarters of the 2nd Army for 24 hours, but at 11.52 on 13 April a radio message reported that these elements had entered Belgrade and occupied the centre of the city. There were better communications between the 1st Panzergruppe and the 2nd Army, and shortly before the message from the 8th Panzerdivision, the army had received a radio transmission from the 1st Panzergruppe reporting its capture of Belgrade from the south, von Kleist having entered the city with the 11th Panzerdivision at 06.30. Thus all three forces reached their objective almost simultaneously.

With the fall of Belgrade, the 1st Panzergruppe was transferred from the 12th Army to the 2nd Army, while the XLVI Corps (mot.) was placed under the direct command of the 1st Panzergruppe for the next phase of the operation, which was the pursuit and destruction of the Yugoslav army’s last field formations, culminating with the capture of Sarajevo on 16 April and the surrender of the Yugoslav army’s final elements on the following day.

Thus the Axis victory had been swift. As early as 14 April the Yugoslav high command had realised that defeat was inevitable, decided to seek an armistice and authorised the army group and army commanders to negotiate local ceasefires. On the same day the commanders of the 2nd Army and 5th Army asked the Germans for terms, but were rejected and informed that only unconditional surrender could form the basis for negotiations. That evening, the high command sent an emissary to the headquarters of the 1st Panzergruppe to request an armistice, and at von Kleist’s recommendation sent the commander of the 2nd Army, von Weichs, travelled to Belgrade to negotiate terms. He arrived on the afternoon of 15 April and drew up an armistice based on unconditional surrender. On 16 April, a Yugoslav delegate arrived in Belgrade, but as he lacked the authority to sign the document, he was given a draft copy of the agreement and an aeroplane was placed at his disposal to fly in authorised representatives of the government. Finally, on 17 April, after only 11 days of fighting, the pre-coup foreign minister, Aleksandar Cincar-Marković, and the commander of the Primorska military district, General Milojko B. Janković, signed the armistice and unconditionally surrendered all Yugoslav troops. The surrender came into effect at 12.00 on the following day, 18 April. At the signing, the Hungarians and Bulgarians were represented only by liaison officers, who did not sign the document as their nations were not officially at war with Yugoslavia. The Italian representative, Colonnello Luigi Buonofati, signed the document after noting that 'the same terms are valid for the Italian army'.

As the 2nd Army and 12th Army took the greater part of Yugoslavia, the Italian 2a Armata had advanced from Istria on two divergent axes from the Trieste area on the left to take Ljubljana and advance past the Sava river to meet the XLIX Gebirgskorps, and from the Fiume area on the right to advance south along the Dalmatian coast to reach Zara. These forces then continued along the coast to take Sibenik and Split before reaching Dubrovnik (taken on 17 April), also the objective of the Italian forces advancing along the coast to the north from northern Albania and the XLVI Corps (mot.) advancing to the south-west from Sarajevo.

The losses sustained by the German attack forces were unexpectedly light. During the twelve days of combat the total casualty figures came to 558 men: 151 were listed as killed, 392 as wounded, and 15 as missing in action. During the XLI Corps (mot.)'s drive on Belgrade, for example, the only officer killed in action fell victim to a civilian sniper’s bullet. The Luftwaffe lost approximately 60 aircraft shot down over Yugoslavia, costing the lives of at least 70 aircrew. The Germans took some 254,000 prisoners, excluding a considerable number of ethnic Bulgarian, Croat, German and Hungarian Yugoslavs who had been conscripted into the Yugoslav army and were quickly released.

The Italian army took comparatively heavy casualties in northern Albania from the Yugoslav offensive there, while the Italian air force lost approximately 10 aircraft shot down, with a further 22 damaged. The Italians took about 30,000 prisoners.

The Hungarian army suffered some 350 casualties (120 killed, 223 wounded and 13 missing in action) from the shelling by Yugoslav riverine forces of its frontier installations and in its attacks upon the Yugoslav frontier forces in Vojvodina, with one quarter of the Hungarian parachute 'battalion' becoming casualties when a transport aeroplane went down during an abortive drop on 12 April. The Hungarians also lost five Fiat fighters and one Weiss WM-21 Sólyom reconnaissance aeroplane during the fighting.

About 1,000 Yugoslav army and several hundreds of air force personnel, as well as one mobile workshop unit of six vehicles, escaped via Greece to Egypt.

In its brief fight, the Yugoslav air force suffered the loss of 49 aircraft to Axis fighters and anti-aircraft fire, with many more damaged beyond repair. These losses cost the lives of 27 fighter pilots and 76 bomber aircrew. Another 85 aircraft were destroyed on the ground by air attack, while many others were destroyed or disabled by their own crews, or crashed during operations or in the course of evacuation flights. Despite these losses, more than 70 Yugoslav aircraft escaped to Allied territory, mostly to Greece, but eight Dornier and Savoia-Marchetti bombers set course for the USSR, which four reached safely. Several dozen of the escapee aircraft were destroyed in a devastating strafing attack by the Italian air force on Paramitia airfield in Greece, with nine bombers and transports making it to Egypt. More than 300 operational, auxiliary and training aircraft were captured and passed to the air force of the newly created Independent State of Croatia, Finland, Romania and Bulgaria.

The Italians captured most of the Yugoslav navy, but the destroyer Zagreb was blown up at Kotor by two of her officers to prevent her capture, and one of the two British-built submarines and two motor torpedo boats succeeded in escaping to Alexandria in Egypt to continue to serve with the Allied cause. Another destroyer, Split, was captured while under construction in the Kotor shipyard, but the Italians were unable to complete her before their own armistice with the Allies in September 1943. Eventually, she was recovered after the war by the Yugoslavs and completed under her original name. Some 10 floatplanes of the Yugoslav naval air arm escaped to Greece, whence nine made it to Egypt, where they formed a squadron under RAF command.

Yugoslavia was then occupied and partitioned by the Axis powers. Some areas of Yugoslavia were annexed by neighbouring Axis countries, in the form of Germany (one area adjacent to Austria), Italy (several areas including most of the Dalmatian islands), Hungary (two areas), Bulgaria (two areas) and Italian-occupied Albania (two areas), and some areas became the Axis puppet state declared even before the defeat of Yugoslavia as the Independent State of Croatia (Nezavisna Drzava Hrvatska, or NDH) under the Croat fascist leader Ante Pavelić. The rump of Serbia became the area for which the Befehlshaber 'Serbien' became responsible, and Montenegro became an Italian protectorate.

The insistence of the Yugoslav army on trying to defend all the borders had assured Yugoslavia’s defeat from the start.

Yet the surrender of 17/18 April was very much not the end of the Yugoslav war as, beginning with the forming of the first partisan battalion near Sisak in Croatia on 22 June and an uprising in Serbia in July, there was continuous resistance to the occupying armies in Yugoslavia until the end of the war. While in the beginning both the communist partisans and royalist Četniks engaged in resistance, the partisans became the main resistance force after the Četniks started to collaborate with the Axis forces in 1942.

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The 2a Armata comprised Generale di Corpo d’Armata Ricardo Balocco’s V Corpo d’Armata with the equivalent of three infantry divisions including Generale di Divisione Pietro Belletti’s 15a Divisione 'Bergamo' and Generale di Divisione Vittorio Zatti’s 57a Divisione 'Lombardia'; Generale di Corpo d’Armata Ricardo Dalmazzo’s VI Corpo d’Armata with Generale di Divisione Emanuele Girlando’s 26a Divisione montagna 'Assietta', Generale di Divisione Furio Monticelli’s 12a Divisione 'Sassari' and Generale di Divisione Vito Ferroni’s 20a Divisione 'Friuli'; Generale di Corpo d’Armata Mario Robotti’s XI Corpo d’Armata with the equivalent of two mountain and two infantry divisions including Generale di Divisione Edoardo Nebbia’s 3a Divisione montagna 'Ravenna', Generale di Divisione Benedetto Fiorenzoli’s 13a Divisione 'Re' and Generale di Divisione Federico Romero’s 14a Divisione 'Isonzo'; Generale di Corpo d’Armata Francesco Zingales’s Corpo d’Armata Motorizzato with Generale di Divisione Gervasio Bitossi’s 133a Divisione corazzata 'Littorio', Generale di Divisione Vittorio Giovannelli’s 9a Divisione autotrasportabile 'Pasubio' and Generale di Divisione Luigi Manzi’s 52a Divisione autotrasportabile 'Torino'; and Generale di Corpo d’Armata Federico Ferrari Orsi’s Corpo d’Armata Celere with Generale di Divisione Cesare Lornaglio’s 1a Divisione celere 'Eugenio di Savoia', Generale di Divisione Carlo Ceriana-Mayneri’s 2a Divisione celere 'Emanuele Filiberto Testa di Ferro', and Generale di Divisione Mario Marazzani’s 3a Divisione celere 'Principe Amedeo Duca d’Aosta'.
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In Albania, Cavallero’s Forze Armate 'Albania' comprised Generale d’Armata Alessandro Pirzio Biroli’s 9a Armata in the north facing Yugoslavia and Generale d’Armata Carlo Geloso’s 11a Armata in the south facing Greece. Tasked with co-operation in 'Unternehmen 25', the 9a Armata's formations were Generale di Divisione Giovanni Vecchi’s XIV Corpo d’Armata with Generale di Divisione Alberto d’Aponte’s 38a Divisione montagna 'Puglie' and Generale di Divisione Emilio Battisti’s 4a Divisione alpina 'Cuneense'; Generale di Corpo d’Armata Giuseppe Pafundi’s XVIII Corpo d’Armata Corazzato with Generale di Divisione Gavino Pizzolato’s 131a Divisione corazzata 'Centauro', Generale di Divisione Francesco Zani’s 18a Divisione 'Messina' and Generale Riccardo Pentimalli’s 32a Divisione montagna 'Marche'; and Generale di Corpo d’Armata Gabriele Nasci’s Settore 'Librazhd' with Generale di Divisione Ernesto Ferone’s 53a Divisione montagna 'Arezzo', Generale di Divisione Giuseppe de Stefanis’s 24a Divisione 'Pinerolo' and Generale di Divisione Paride Negri’s 41a Divisione 'Firenze'.
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The 2nd Army comprised General Ludwig Kübler’s XLIX Gebirgskorps with Generalleutnant Hubert Lanz’s 1st Gebirgsdivision, Generalleutnant Karl Strecker’s 79th Division and Generalleutnant Emmerich von Nagy’s 538th Division zbV; General Hans-Wolfgang Reinhard’s LI Corps with Generalleutnant Erich Marcks’s 101st leichte Infanteriedivision, Generalleutnant Rudolf Sintzenich’s 132nd Division and Generalleutnant Benignus Dippold’s 183rd Division; and General Heinrich-Gottfried von Vietinghoff-Scheel’s XLVI Corps (mot.) with Generalmajor Erich Brandenberger’s 8th Panzerdivision, Generalmajor Friedrich Kühn’s 14th Panzerdivision and Generalleutnant Sigfrid Henrici’s 16th Division (mot.). There was also General Kurt von Breisen’s LII Corps with Generalleutnant Willi Schneckenburg’s 125th Division, but this did not become operational until 15 April.
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The 12th Army comprised General Georg Stumme’s XL Corps (mot.) with Generalleutnant Alfred Ritter von Hubicki’s 9th Panzerdivision, Generalleutnant Bruno Bieler’s 73rd Division and SS-Obergruppenführer und General der Waffen-SS Joseph Dietrich’s Leibstandarte SS 'Adolf Hitler'); General Georg-Hans Reinhardt’s XLI Corps (mot.) with SS-Gruppenführer und Generalleutnant der Waffen-SS Paul Hausser’s SS Division (mot.) 'Reich' and Oberst Wilhelm-Hunold von Stockhausen’s Infanterieregiment (mot.) 'Grossdeutschland' assembled in western Bulgaria to descend on Belgrade; General Franz Böhme’s XVIII Corps assembled in south-western Bulgaria to pass via Strumica and the Vardar river valley in the extreme south-east of Yugoslavia straight into northern Greece; and von Kleist’s 1st Panzergruppe assembled to the north-west and south-west of Sofia, the Bulgarian capital, to attack in the direction of Nis and Skopje. The 1st Panzergruppe comprised General Gustav von Wietersheim’s XIV Corps (mot.) with Generalmajor Gustav Fehn’s 5th Panzerdivision, Generalleutnant Ludwig Crüwell’s 11th Panzerdivision, Generalleutnant Friedrich-Georg Eberhardt’s 60th Division (mot.), Generalleutnant Karl Eglseer’s 4th Gebirgsdivision and Generalleutnant Otto Gabcke’s 294th Division.