Invasion of Yugoslavia

1941 Axis campaign during World War II

Continued anti Axis resistance and beginning of World War II in Yugoslavia
| territory = Occupation of YugoslaviaPartition of Yugoslavia between the AxisCreation of pro Axis puppet regimes
| combatant1 = Axis:
| combatant2 = Kingdom of Yugoslavia
| commander1 =
| commander2 =
| strength1 = Germany:337,096875 tanks990 aircraftItaly:300,000 in 22 divisions666 aircraftHungary:9 brigades6 air squadrons
| strength2 = 700,000(400,000 ill prepared)110–200 tanks(50–54 of which were modern)460–505 aircraft(including 103 modern bombers and 107 modern fighters)
| casualties1 = Germany:151 killed392 wounded15 missing40 aircraft shot downItaly:800 killed2,500 wounded and "without waiting for possible declarations of loyalty of the new government". Hungary had joined the Tripartite Pact on 20 November 1940. On 12 December, it also concluded a treaty with Yugoslavia calling for "permanent peace and eternal friendship". The Hungarian leadership was split after Germany's War Directive 25 was delivered on 27 March 1941. Regent Miklós Horthy and the military favoured taking part in the invasion of Yugoslavia and mobilized the following day. 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 1 April, Yugoslavia redesignated its Assault Command as the Chetnik Command, named after the Serb guerrilla forces from World War I, which had resisted the Central Powers. The command was intended to lead a guerrilla war if the country was occupied. Its headquarters was transferred from Novi Sad to Kraljevo in south central Serbia on 1 April. On 2 April, the German ambassador having already been recalled for "talks", the remaining embassy staff were ordered to leave the capital and to warn the embassies of friendly nations to likewise evacuate. That sent the unmistakable message that Yugoslavia was about to be invaded. On 3 April, Hitler issued War Directive 26 detailing the plan of attack and command structure for the invasion as well as promising Hungary territorial gains. The same day Teleki killed himself. 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 was realized, and Hungary joined the invasion, its army crossing into Yugoslavia the following day.

The invasion was spearheaded by the German 2nd Army with elements of the 12th Army, First Panzer Group, and an independent panzer corps combined with overwhelming Luftwaffe support. The 19 German divisions included five panzer divisions, two motorised infantry divisions and two mountain divisions. The German force also included three well equipped independent motorised infantry regiments and was supported by over 750 aircraft. The Italian 2nd Army and 9th Army committed a total of 22 divisions and 666 aircraft to the operation. The Hungarian 3rd Army also participated in the invasion, with support available from over 500 aircraft. During the April War, the Führer Headquarters (FHQ) was codenamed Frühlingssturm (Spring Storm) and consisted of the Führersonderzug (Special Führer's Train) codenamed "Amerika" stationed in Mönichkirchen alongside the special train "Atlas" of the Armed Forces Operations Staff (Wehrmachtführungsstabes, WFSt). "Atlas" did not arrive at Mönichkirchen until 11 April, well after operations were underway, and "Amerika" only arrived the following day. Mönichkirchen was chosen because a nearby rail tunnel could provide shelter in the event of air attack. Both trains returned to Berlin on 26 April. After the Italian invasion in the northwest began, King Victor Emmanuel III moved to a villa owned by the Pirzio Biroli family at Brazzacco, near Moruzzo, in order to be close to the front. Germany attacked Yugoslavia from bases in three countries besides itself: Hungary, Romania, and Bulgaria. German troops entered each of these countries under different pretenses and at different times. The first country to receive a German military mission was Romania. Ostensibly to train the Romanian armed forces, its real purpose was to protect Romania's petroleum resources and prepare for an attack on the Soviet Union. The Wehrmacht entered Bulgaria more circumspectly, first with the intention of providing aerial defense against any force attacking Romania's oilfields and later with that of invading Greece in support of Italy. German troops did not enter Hungary until the attack on Yugoslavia was already planned and Hungary's participation had been secured.

King Carol II of Romania, starting from the cession of Bessarabia and Northern Bukovina to the Soviet Union, proposed in a letter to Adolf Hitler on 2 July 1940 that Germany send a military mission to Romania. The Romanian government asked that a mission be sent urgently on 7 September 1940, the day after Carol's abdication. The decision to aid Romania was taken on 19 September, and Hungary was asked to provide transit to German soldiers on 30 September. The first troops entered Romania on 10 October. They entered Bucharest two days later (12 October) to shouts of Heil! The official explanation for the presence of German troops was that they were there to train the Romanian army. Hitler's directive to the troops on 10 October had stated that "it is necessary to avoid even the slightest semblance of military occupation of Romania." In the second half of October, the Romanian leader, Ion Antonescu, asked that the military mission be expanded. The Germans happily obliged the request, since the oil fields and refineries at Ploiești were vital to their war effort. Romania was also an important launching point for an attack on the Soviet Union, which made the presence of German troops a violation of the Molotov–Ribbentrop Pact of 23 August 1939. By the middle of November, the 13th Motorised Infantry Division had been assembled in Romania and reinforced by the 4th Panzer Regiment, engineers and signal troops, as well as six fighter and two reconnaissance Luftwaffe squadrons, and some antiaircraft artillery. A total of seventy batteries of artillery were moved into Romania. On 23 November, Romania signed the Tripartite Pact. At the time Germany informed Romania that she would not be expected to participate in an attack on Greece, but that Germany wanted to use Romanian territory to provide a base for a German attack. On 24 November, Antonescu met with Wilhelm Keitel, chief of the Oberkommando der Wehrmacht, to discuss common defense. As a result of this meeting, the 16th Panzer Division was sent to Romania in late December. The 12th Army and First Panzer Group, along with heavy bridging equipment for the planned crossing of the Danube, followed in January 1941. By January 1941 the total number of German effectives in Romania was 170,639. Those elements of the 12th Army that were to invade Yugoslavia from Romania assembled near Timișoara (Temeschwar). Between November 1940 and February 1941, the Luftwaffe gradually moved 135 fighters and reconnaissance aircraft into Romania (in 22–26 squadrons). In early April 1941 they moved a further 600 aircraft from France, Africa, and Sicily into Romania and Bulgaria in a period of ten days. The fighter and reconnaissance craft were sent to fields in Arad, Deva, and Turnu Severin. On 12 February Britain broke off diplomatic relations with Romania on the grounds that it was an enemy occupied country.

Two events in early November 1940 convinced Hitler of the need to station troops, especially the Luftwaffe, in Bulgaria. The first was false reports that the British were constructing an airfield on Lemnos, from which they could bomb Ploiești. The second was the beginning of British air raids originating from Greek bases against Italian shipping on 6 November. Planning for the German invasion of Greece from Bulgaria began on 12 November. Already on 13 November, the Soviets were (incorrectly) accusing the Germans of having troops in neutral Bulgaria. On 18 November, Tsar Boris III of Bulgaria met with Hitler and promised to participate in an attack on Greece, but only at the last moment. Shortly thereafter a secret German team under Colonel Kurt Zeitzler entered Bulgaria to establish fuel depots, arrange for troop billeting and scout the terrain. They were soon followed by hundreds of Luftwaffe personnel to establish air observation stations. By the end of December over a thousand German troops in civilian clothing were active in Bulgaria, although the latter's government continued to deny it. Bombers and dive bombers were also gradually moved into Bulgaria, beginning in November. By the end of March 1941, the Luftwaffe had 355 aircraft in the country. On 17 February 1941, Bulgaria signed a non aggression pact with Turkey, paving the way for its adherence to the Tripartite Pact, which was signed by Prime Minister Bogdan Filov in Vienna on 1 March. When Ivan V. Petrov, member of the National Assembly from Yablanitsa, asked why the Assembly had not been consulted, Filov pointed out that the constitution only required parliamentary approval prior to ratification. The signing was ratified by a vote in the Assembly of 140 to 20. The first German troops crossed the Danube from Romania on 28 February, a day before Bulgaria joined the pact. The greater part of the 12th Army, augmented by VIII. Fliegerkorps, crossed the Danube on 2 March. They were welcomed by the Russophile population, who believed that Germany and the Soviet Union were allied. The 12th Army was originally deployed solely for an attack on Greece. After receiving Directive No. 25, which projected an invasion of Yugoslavia in the direction of Belgrade on 8 April, the force was redeployed in three groups: one along the Turkish border, one along the Greek border and one along the Yugoslav border. Motorized transport was brought in from Romania to achieve this feat in a few days.

Although German troops had been refused the right to transit Hungary for the invasion of Poland in 1939, they were permitted to pass through Hungary as civilians on their way to Romania in 1940. In September 1940 the Hungarian legation in Berlin had granted over 6,500 transit visas to Germans traveling to Romania. On 30 September, shortly after the signing of the Tripartite Pact, Ribbentrop and General Keitel asked the Hungarian foreign minister, István Csáky, who was in Vienna, to grant the Germans use of transit facilities for German military "study groups" to pass through to Romania. They were still awaiting final confirmation on 3 October. The arrangement agreed was that six trains would pass through Hungary at night carrying German soldiers in sealed cars. They would not be allowed out, and they would not have any rail transportation officers (RTOs) or supply officers with them. According to György Barcza, the Hungarian ambassador in London, answering the British government's query, it was Romania that had made the request. In his notes, Barcza indicated that the British had declared that "if Hungary were to permit German troops to pass through Hungarian territory against Yugoslavia, Britain would break off diplomatic relations, indeed might declare war on us." The first German troops began their passage through Hungary on 8 October. Despite some official denials, the troops movements were reported by Reuters and the American ambassador received a full report. According to contemporary British intelligence, three divisions had passed through Hungary to Romania by 2 November. On 20 November, Hungarian Prime Minister Pál Teleki signed the Tripartite Pact after a meeting with Hitler in Berchtesgarden. At the meeting, Hitler spoke of his intention to aid Italy against Greece, thereby preparing the Hungarians for his future demands. On 13 December 1940—the day after the Hungaro Yugoslav Non Aggression Pact and the day Hitler issued Führer Directive No. 20—major German troop movements began. The Germans had initially promised to supply 180 locomotives for the transfers, but later the Hungarians were complaining that only 130 had arrived. On 24 December, István Horthy, President of Hungarian State Railways (HSR), demanded negotiations before implementing requested German increases, but Ambassador Otto von Erdmannsdorf informed him that it had all been settled in Vienna by Keitel and Csáky. The German traffic was so large that on 28 December the HSR had to suspend travel on all its trains for several days on account of a shortage of coal. Hungarian officials tried to meet all German demands without going further than the governments had agreed. Even sabotage was used on occasion to prevent having to give the Germans more support than required. On 18 January 1941 an agreement was reached to store German supplies in Hungarian warehouses under Hungarian guard, with only a German officer in Budapest to serve as a liaison. These supplies were to be used in the campaign against Greece. On 27 March 1941, Hitler informed the Hungarian ambassador, Döme Sztójay, and gave an official proposal to Hungary for participation in the attack on Yugoslavia. Hitler confidentially told Miklós Horthy that Germany fully recognizes the Hungarian territorial claims in relation to Yugoslavia and that he can take Bačka and Banat, and added "take as much as you want". Horthy mostly agreed and accepted Hitler's suggestions. A Hungarian response was hammered out in council and delivered the following day (28 March). On 30 March, General Friedrich Paulus arrived in Budapest and met with Henrik Werth, chief of the Hungarian general staff, and Major General László Deseő. The Hungarians proposed they mobilize five divisions for the attack on Yugoslavia. Two were to be held in reserve, while the First, Fifth and Mobile Corps were to conduct the main attack on Subotica (Szabadka), with a secondary operation east of the river Tisza. Because of Romania's request that Hungarian troops not operate in the Banat, Paulus modified the Hungarian plan and kept their troops west of the Tisza. This final plan "was put down in map form", according to Paulus' account, and must have been telephoned to Berlin immediately so as to make into Operational Order No. 25, issued by Walther von Brauchitsch that same day. This final plan committed one Hungarian corps of three brigades west of the Danube from Lake Balaton to Barcs, and twelve brigades (nine on the front and three in reserve) for an offensive in Bačka (Bácska). The Danube Flotilla was to cover the flanks, and the air force was to stand by for orders. The "Carpathian Group", composed of Eighth Corps, the 1st Mountain Brigade and the 8th Border Guard (Chasseur) Brigade, was mobilized on the Soviet border, with the Mobile Corps held in reserve. These arrangements were agreed to by Werth, he later claimed, "on the basis of the authorization received" on 28 April—although this was not the government's view of what had been authorized. Werth applied for permission to mobilize on 1 April, since a mobilization order had to be approved by the cabinet and issued by the regent over the signature of the minister of defense. Werth expected the Germans to begin operations, with the use of Hungarian territory and communications, on 12 April and the Hungarians to complete mobilization by 6 April and begin their offensive on the 15th. A meeting of the Supreme Defense Council was convened for 1 April to discuss Werth's request. After a long debate, it approved his mobilization plan, but refused to place Hungarian troops under German command and restricted Hungarian operations to the occupation of territory abandoned by the Yugoslavs. On 2 April Germany responded that the Paulus–Werth agreement was final, and German staff officers began arriving in Budapest that day. That same day the British informed Hungary that she would be treated as an enemy state if Germany made use of her territory or facilities in an attack on Yugoslavia. On the morning of 3 April, Pál Teleki committed suicide; the regent immediately cancelled the mobilization order already given except for the Border Guard and the Mobile Corps, which prompted Werth to resign. Horthy then authorized the mobilization of the Fourth and Fifth Corps and the Mountain Brigade, and Werth withdrew his resignation. This occurred so late in the day that zero hour for mobilization to begin was given as midnight of 5 April. On the morning of 3 April, German units, including tanks and aircraft, bound for Romania passed openly through Budapest.

The Italian 2nd Army and 9th Army committed a total of 22 divisions to the operation, comprising around 300,000 troops. The Italian 2nd Army was commanded by Generale designato d’Armata (acting General) Vittorio Ambrosio, and consisted of one fast corps (Celere Corps), one motorised corps (Motorised Corps) and three infantry corps (V Corps, VI Corps, and XI Corps), and was assembled in northeastern Italy, attacking from Istria and the Julian March along the border with Slovenia and Croatia. The 2nd Army was supported by a motorised engineer regiment including three bridging battalions, a chemical battalion, fifteen territorial battalions, and two garrison battalions. V Corps support units included three motorised artillery regiments comprising thirteen battalions, four machine gun battalions (two motorised and two pack animal), three Blackshirt legions of battalion size, a motorised anti aircraft battalion, a sapper assault battalion and a road construction battalion. VI Corps included four motorised artillery regiments with a total of sixteen battalions, two machine gun battalions (one motorised, one pack animal) and a motorised anti aircraft regiment. XI Corps included one motorised artillery regiment comprising four battalions, three machine gun battalions (one motorised, one pack animal and one static), and six Blackshirt legions of battalion size. The Motorised Corps was supported by a motorised artillery regiment consisting of three battalions, and a motorised engineer battalion. In Albania, the elements of the Italian 9th Army that were involved in the campaign were commanded by Generale d’Armata (General) Alessandro Pirzio Biroli, and consisted of two infantry corps and some sector troops assembled in northern Albania. XIV Corps was supported by a cavalry regiment, three Border Guard battalions, a Finance Guard battalion and two military police battalions. The XVII Corps included the Diamanti Blackshirt group which incorporated six Blackshirt regiments comprising two battalions each, the Albanian raised Skanderbeg Blackshirt regiment of two battalions, another Blackshirt regiment of two battalions, a cavalry regiment, a Bersaglieri motorcycle battalion, three Border Guard battalions, one Finance Guard battalion, a motorised artillery regiment of three battalions, a military police battalion, and a tank company equipped with Fiat M13/40 light tanks. The Librazhd Sector included a motorised artillery regiment of four battalions, a bicycle mounted Bersaglieri regiment, a cavalry regiment, the Biscaccianti Blackshirt group which incorporated two Blackshirt regiments with a total of five battalions, the regimental sized Agostini Blackshirt Forest Militia, and the Briscotto group, a regimental sized formation consisting of one Alpini battalion and two Finance Guard battalions. The Zara garrison numbered about 9,000 men under the overall command of Generale di Brigata (Brigadier) Emilio Giglioli. The garrison consisted of two main groupings and an assortment of supporting units. The two main groupings were the regimental sized Fronte a Terra (Land Front), which comprised three static machine gun battalions and a bicycle mounted Bersaglieri battalion, and the battalion strength Fronte a Mare (Sea Front), which consisted of two machine gun companies, an anti aircraft battery, a coastal artillery battery and a naval artillery battery. Supporting units consisted of an artillery regiment of three battalions, two independent artillery battalions, a machine gun battalion, a motorised anti aircraft battalion (less one battery), an engineer battalion, a company of Blackshirts, and a company of L3/35 tankettes.

The Yugoslav forces consisted of more than 33 divisions of the Royal Yugoslav Army (, VKJ), four air brigades of the Royal Yugoslav Air Force (, VVKJ) with more than 400 aircraft, and the small Royal Yugoslav Navy (, KJRM) centred around four destroyers and four submarines based on the Adriatic coast and some river monitors on the Danube. The VKJ was heavily reliant on animal powered transport, was only partly mobilised at the time of the invasion, and had only 50 tanks that could engage German tanks on an equal basis. The VVKJ was equipped with a range of aircraft of Yugoslav, German, Italian, French and British design, including less than 120 modern fighter aircraft.

Formed after World War I, the VKJ was still largely equipped with weapons and material from that era, although some modernization with Czech equipment and vehicles had begun. Of about 4,000 artillery pieces, many were aged and horse drawn, but about 1,700 were relatively modern, including 812 Czech 37mm and 47mm anti tank guns. There were also about 2,300 mortars, including 1600 modern 81mm pieces, as well as twenty four 220 and 305mm pieces. Of 940 anti aircraft guns, 360 were 15 mm and 20 mm Czech and Italian models. All of these arms were imported, from different sources; the various models often lacked proper repair and maintenance facilities. The only mechanized units were six motorized infantry battalions in the three cavalry divisions, six motorized artillery regiments, two tank battalions equipped with 110 tanks, one of which had Renault FT models of First World War origin and the other 54 modern French Renault R35 tanks, plus an independent tank company with eight Czech T 32 (Š I D) tank destroyers. Some 1,000 trucks for military purposes had been imported from the United States of America in the months just preceding the invasion. Fully mobilized, the Yugoslav Army fielded 28 infantry divisions, three cavalry divisions, and 35 independent regiments. Of the independent regiments, 16 were in frontier fortifications and 19 were organized as combined regiments, or "Odred", around the size of a reinforced brigade. Each Odred had one to three infantry regiments and one to three artillery battalions, with three organised as "alpine" units. The German attack, however, caught the army still mobilizing, and only some 11 divisions were in their planned defense positions at the start of the invasion. The Yugoslavs had delayed full mobilisation until 3 April in order not to provoke Hitler. The units were filled to between 70 and 90 percent of their strength as mobilization was not completed. The Yugoslav Army was about 1,200,000 in total as the German invasion commenced.