Invasion of Yugoslavia

The invasion of Yugoslavia, also known as the April War (Aprilski rat) or Operation 25, was a German-led attack on the Kingdom of Yugoslavia by the Axis powers which began on 6 April 1941 during World War II. The order for the invasion was put forward in "Führer Directive No. 25", which Adolf Hitler issued on 27 March 1941, following the Yugoslav coup d'état.

The invasion commenced with an overwhelming air attack on Belgrade and facilities of the Royal Yugoslav Air Force (VVKJ) by the Luftwaffe (German Air Force) and attacks by German land forces from southwestern Bulgaria. These attacks were followed by German thrusts from Romania, Hungary and the Third Reich (modern-day Austria). Italian forces were limited to air and artillery attacks until 11 April, when the Italian army attacked towards Ljubljana (in modern-day Slovenia) and through Istria and Lika and down the Dalmatian coast. On the same day, Hungarian forces entered Yugoslav Bačka and Baranya, but like the Italians they faced practically no resistance. A Yugoslav attack into the northern parts of the Italian protectorate of Albania met with initial success, but was inconsequential due to the collapse of the rest of the Yugoslav forces.

The invasion ended when an armistice signed on 17 April 1941, based on the unconditional surrender of the Royal Yugoslav Army, which came into effect at noon on 18 April. Yugoslavia was then occupied and partitioned by the Axis powers. Some areas of Yugoslavia were annexed by neighboring Axis countries, some areas remained occupied, and in other areas Axis puppet states such as the Independent State of Croatia (Nezavisna Država Hrvatska, or NDH) were created. Along with Italy's failed invasion of Greece on 28 October 1940, and the German-led invasion of Greece (Operation Marita) and invasion of Crete (Operation Merkur), the invasion of Yugoslavia was part of the German Balkan Campaign (Balkanfeldzug).

Prelude
In October 1940, Fascist Italy had attacked Greece only to be forced back into Albania. German dictator Adolf Hitler recognised the need to go to the aid of his ally, Italian dictator Benito Mussolini. Hitler did this not only to restore diminished Axis prestige, but also to prevent the United Kingdom from being able to bomb the Romanian oilfields from which Germany obtained most of her oil.

Following agreements with Hungary, Romania and Bulgaria that they would join the Axis, Hitler put pressure on Yugoslavia to join the Tripartite Pact. The Regent, Prince Paul of Yugoslavia and his cabinet, succumbed to this pressure on 25 March 1941. This move was unpopular with the Serbian-dominated officer corps of the military and some segments of the public: a large part of the Serbian population, as well as liberals and Communists. A coup d'état was launched on 27 March 1941 by mainly Serbian military officers, and the Regent was replaced on the throne by the under-age prince, who was declared of age and proclaimed King Peter II of Yugoslavia.

Upon hearing news of the coup in Yugoslavia, Hitler called his military advisers to Berlin on 27 March. On the same day as the coup he issued Führer Directive 25 which called for Yugoslavia to be treated as a hostile state. Hitler took the coup as a personal insult, and was so angered that he was determined, in his words, "to destroy Yugoslavia militarily and as a nation" (Jugoslawien militärisch und als Staatsgebilde zu zerschlagen), and to do so "without waiting for possible declarations of loyalty of the new government".

On 1 April Yugoslavia redesignated its Assault Command as the Chetnik Command, after the Serbian and Macedonian guerrilla forces from World War I which had resisted the Central Powers. The command was intended to lead a guerrilla war should the country be 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 was ordered to leave the capital and to warn the embassies of friendly nations to likewise evacuate. This sent the unmistakable message that Yugoslavia was about to be invaded.

Hungary
Hungary had joined the Tripartite Pact on 20 November 1940. The following month on 12 December it also concluded a treaty with the Kingdom of 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 cooperation with the Germans. On 3 April, War Directive 26 was issued detailing the plan of attack and command structure for the invasion as well as promising Hungary territorial gains. The same day Teleki committed suicide by shooting 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.

Axis order of battle
The invasion was spearheaded by the German 2nd Army, with elements of the 12th Army, a 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.

Royal Yugoslav armed forces
The Yugoslav forces consisted of more than 33 divisions of the Royal Yugoslav Army (Vojska Kraljevska Jugoslavije, VKJ), four air brigades of the Royal Yugoslav Air Force (Vazduhoplovstvo Vojske Kraljevine Jugoslavije, VVKJ) with more than 400 aircraft, and the small Royal Yugoslav Navy (Kraljevska Jugoslovenska Ratna Mornarica, 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.

Equipment and organization
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, which meant that 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-17s models of First World War origin and the other 54 modern French Renault R35 tanks, plus an independent tank company with eight Czech SI-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 could have put 28 infantry divisions, three cavalry divisions, and 35 independent regiments in the field. 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 offend Hitler. The units were filled to between 70 and 90 percent of their strength as mobilization was not completed. The strength of the Yugoslav Army was about 1,200,000 as the German invasion got underway.

The VVKJ had a strength of 1,875 officers and 29,527 other ranks, including some 2,000 pilots, had over 460 front-line aircraft of domestic (notably the IK-3), German, Italian, French, and British origin, of which most were modern types. Organized into 22 bomber squadrons and 19 fighter squadrons, the main aircraft types in operational use included 73 Messerschmitt Bf 109 E, 47 Hawker Hurricane I (with more being built under licence in Yugoslavia), 30 Hawker Fury II, 11 Rogozarski IK-3 fighters (plus more under construction), 10 Ikarus IK-2, 2 Potez 63, one Messerschmitt Bf 110C-4 (captured in early April due to a navigational error) and one Rogozarski R 313 fighters, 69 Dornier Do 17 K (including 40 plus licence-built), 61 Bristol Blenheim I (including some 40 licence-built) and 40 Savoia Marchetti SM-79 K bombers. Army reconnaissance units comprised seven Groups with 130 obsolete Yugoslav-built Breguet 19 and Potez 25 light bombers. There were also some 400 trainer and auxiliary aircraft. The Naval Aviation units comprised 75 aircraft in eight squadrons equipped with, amongst other auxiliary types, 12 German-built Dornier Do 22 K and 15 Rogozarski SIM-XIV-H locally designed and built maritime patrol float-planes.

The aircraft of the Yugoslav airline Aeroput, consisting mainly of six Lockheed Model 10 Electras, three Spartan Cruisers, and one de Havilland Dragon were mobilised to provide transport services to the VVKJ.

The KJRM was equipped with one elderly ex-German light cruiser (suitable only for training purposes), one large modern destroyer flotilla leader of British design, three modern destroyers of French design (two built in Yugoslavia plus another still under construction), one seaplane tender, four modern submarines (two older French-built and two British-built) and 10 modern motor torpedo boats (MTBs), of the older vessels, there were six ex-Austrian Navy medium torpedo boats, six mine-layers, four large armoured river monitors and various auxiliary craft.

Deployment
The Yugoslav Army was organized into three army groups and the coastal defense troops. The 3rd Army Group was the strongest with the 3rd, 3rd Territorial, 5th and 6th Armies defending the borders with Romania, Bulgaria and Albania. The 2nd Army Group with the 1st and 2nd Armies, defended the region between the Iron Gates and the Drava River. The 1st Army Group with the 4th and 7th Armies, composed mainly of Croatian troops, was in Croatia and Slovenia defending the Italian, German (Austrian) and Hungarian frontiers.

The strength of each "Army" amounted to little more than a corps, with the three Army Groups consisting of the units deployed as follows; The 3rd Army Group's 3rd Army consisted of four infantry divisions and one cavalry odred; the 3rd Territorial Army with three infantry divisions and one independent motorized artillery regiment; the 5th Army with four infantry divisions, one cavalry division, two odred and one independent motorized artillery regiment and the 6th Army with three infantry divisions, the two Royal Guards brigades (odred) and three infantry odred. The 2nd Army Group's 1st Army had one infantry and one cavalry divisions, three odred and six frontier defence regiments; the 2nd Army had three infantry divisions and one frontier defence regiment. Finally, the 1st Army Group consisted of the 4th Army, with three infantry divisions and one odred, whilst the 7th Army had two infantry divisions, one cavalry division, three mountain odred, two infantry odred and nine frontier defence regiments. The Strategic, "Supreme Command" Reserve in Bosnia comprised four infantry divisions, four independent infantry regiments, one tank battalion, two motorized engineer battalions, two motorized heavy artillery regiments, 15 independent artillery battalions and two independent anti-aircraft artillery battalions. The Coastal Defence Force, on the Adriatic opposite Zadar comprised one infantry division and two odred, in addition to fortress brigades and anti-aircraft units at Šibenik and Kotor.

On the eve of invasion, clothing and footwear were available for only two-thirds or so of the potential front-line troops and only partially for other troops; some other essential supplies were available for only a third of the front-line troops; medical and sanitary supplies were available for only a few weeks, and supplies of food for men and feed for livestock were available for only about two months. In all cases there was little or no possibility of replenishment.

Beyond the problems of inadequate equipment and incomplete mobilization, the Yugoslav Army suffered badly from the Serbo-Croat schism in Yugoslav politics. "Yugoslav" resistance to the invasion collapsed overnight. The main reason was that none of the subordinate national groups, including Slovenes and Croats, were prepared to fight in defence of a Serbian Yugoslavia. Also, so that the Slovenes did not feel abandoned, defences were built on Yugoslavia's northern border when the natural line of defence was much further south, based on the rivers Sava and Drina. The only effective opposition to the invasion was from wholly Serbian units within the borders of Serbia itself. The Germans, thrusting north-west from Skoplje, were held up at Kacanik Pass and lost several tanks (P39, Buckley C "Greece and Crete 1941" HMSO 1977). In its worst expression, Yugoslavia's defenses were badly compromised on 10 April 1941, when some of the units in the Croatian-manned 4th and 7th Armies mutinied, and a newly formed Croatian government hailed the entry of the Germans into Zagreb the same day. The Serbian General Staff were united on the question of Yugoslavia as a "Greater Serbia", ruled, in one way or another, by Serbia. On the eve of the invasion, there were 165 generals on the Yugoslav active list. Of these, all but four were Serbs.

Operations
Professor Jozo Tomasevich and others divide the invasion and resultant fighting into two phases. The first phase encompasses the Luftwaffe's devastating air assault on Belgrade and airfields of the Royal Yugoslav Air Force of 6 April, and an initial thrust of the German XL Panzer Corps from Bulgaria towards Skopje that commenced the same day. This was followed by the assault of the German XIV Panzer Corps from Bulgaria towards Niš on 8 April. On 10 April, four more thrusts struck the Yugoslav Army; the XLI Panzer Corps from Romania towards Belgrade, the XLVI Panzer Corps from Hungary across the Drava, the LI Infantry Corps from Austria towards Zagreb, and the XLIX Mountain Corps from Austria towards Celje. By the end of that day, the Yugoslav Army was disintegrating, and was in retreat or surrendering right across the country, with the exception of the forces on the Albanian frontier. Italy and Hungary joined the ground offensive on 11 April. The Italian part in the ground offensive began when their 2nd Army attacked from northeastern Italy towards Ljubjana and down the Dalmatian coast, meeting virtually no resistance. On the same day, the Hungarian 3rd Army crossed the Yugoslav border and advanced toward Novi Sad, but like the Italians, they met no serious resistance. On 12 April, German troops captured Belgrade, and Ljubjana fell to the Italians. On 14 and 15 April, King Peter and the government flew out of the country, and the Yugoslav Supreme Command was captured by the Germans near Sarajevo. The surrender was signed on 17 April, and came into effect at noon on 18 April.

Air operations
Following the Belgrade Coup on 25 March 1941, the Yugoslav armed forces were put on alert, although the army was not fully mobilised for fear of provoking Hitler. The VVKJ command decided to disperse its forces away from their main bases to a system of 50 auxiliary airfields that had previously been prepared. However many of these airfields lacked facilities and had inadequate drainage which prevented the continued operation of all but the very lightest aircraft in the adverse weather conditions encountered in April 1941.

Despite having, on paper at any rate, a substantially stronger force of relatively modern aircraft than the combined British and Greek air forces to the south, the VVKJ could simply not match the overwhelming Luftwaffe and Regia Aeronautica superiority in terms of numbers, tactical deployment and combat experience.

The bomber and maritime force hit targets in Italy, Germany (Austria), Hungary, Romania, Bulgaria, Albania and Greece, as well as attacking German, Italian and Hungarian troops. Meanwhile the fighter squadrons inflicted not insignificant losses on escorted Luftwaffe bomber raids on Belgrade and Serbia, as well as upon Regia Aeronautica raids on Dalmatia, Bosnia, Herzegovina and Montenegro. The VVKJ also provided direct air support to the hard pressed Yugoslav Army by strafing attacking troop and mechanized columns in Croatia, Bosnia and Serbia (sometimes taking off and strafing the troops attacking the very base being evacuated).

Little wonder then that after a combination of air combat losses, losses on the ground to enemy air attack on bases and the overrunning of airfields by enemy troops, that after 11 days the VVKJ almost ceased to exist. It must, however, be noted that between 6 and 17 April 1941 the VVKJ received an additional eight Hurricane Is, six Dornier Do-17Ks, four Blenheim Is, two Ikarus IK 2s, one Rogozarski IK-3 and one Messerschmitt Bf 109 from the local aeronautical industry's aircraft factories and work-shops.

The VVKJ's Dornier bomber force provides an illustrative case in point. At the beginning of the April war, the VVKJ was armed with some 60 German designed Do 17Ks, purchased by Yugoslavia in the autumn of 1938, together with a manufacturing licence. The sole operator was 3 vazduhoplovni puk (3rd bomber regiment) composed of two bomber groups; the 63rd Bomber Group stationed at Petrovec airfield near Skopje and the 64th Bomber Group stationed at Milesevo airfield near Priština. Other auxiliary airfields had also been prepared to aid in dispersal.

During the course of hostilities, the State Aircraft Factory in Kraljevo managed to produce six more aircraft of this type. Of the final three, two were delivered to the VVKJ on 10 April and one was delivered on 12 April 1941.

On 6 April, Luftwaffe dive-bombers and ground-attack fighters destroyed 26 of the Yugoslav Dorniers in the initial assault on their airfields, but the remaining aircraft were able to effectively hit back with numerous multi-ship attacks on German mechanized columns and upon Bulgarian airfields. By the end of the campaign total Yugoslav losses stood at four destroyed in aerial combat and 45 destroyed on the ground. On 14 and 15 April, the seven remaining Do 17K flew to Nikšić airfield in Montenegro and took part in the evacuation of King Petar II and members of the Yugoslav government to Greece. During this operation, Yugoslav gold reserves were also airlifted to Greece by the seven Do 17s, as well as by SM-79Ks and Lockheed Electra's but after completing their mission, five Do 17Ks were destroyed on the ground when Italian aircraft attacked the Greek-held Paramitia airfield. Only two Do 17Ks escaped destruction in Greece and later joined the British Royal Air Force (RAF) in the Kingdom of Egypt.

At 16:00 on the 15 April the C-in-C of Luftflotte 4, Generaloberst Alexander Löhr received orders from Hermann Göring to wind down the air-offensive and transfer the bulk of the dive-bomber force to support the campaign in Greece.

A total of 18 bomber, transport and maritime patrol aircraft (two Dornier Do 17Ks, four Savoia Marchetti SM-79Ks, three Lockheed Electra's, eight Dornier Do-22Ks and one Rogozarski SIM-XIV-H) succeeded in escaping to the Allied base in Egypt at the end of the campaign.

Bombing of Belgrade
Luftflotte 4 of the Luftwaffe, with a strength of seven Combat Formations (Kampfgruppen) had been committed to the campaign in the Balkans. Hitler, infuriated at Yugoslavia's defiance, ordered the implementation of Operation Punishment (Unternehmen Strafgericht). At 07:00 on 6 April the Luftwaffe opened the assault on Yugoslavia by conducting a saturation-type bombing raid on the capital. Flying in relays from airfields in Austria and Romania, 300 aircraft, of which a quarter were Junkers Ju 87 Stukas, protected by a heavy fighter escort began the attack. The dive-bombers were to silence the Yugoslav anti-aircraft defences while the medium bombers consisting mainly Dornier Do 17s and Junkers Ju 88 attacked the city. The initial raid was carried out at 15 minute intervals in three distinct waves, each lasting for approximately 20 minutes. Thus, the city was subjected to a rain of bombs for almost one and a half hours. The German bombers directed their main effort against the center of the city, where the principal government buildings were located. The medium bomber Kampfgruppen continued their attack on the city for several days while the Stuka dive bomber wings (Stukageschwaders) were soon diverted to Yugoslav airfields.

When the attack was over, some 4,000 inhabitants lay dead under the debris. This blow virtually destroyed all means of communication between the Yugoslav high command and the forces in the field, although most of the elements of the general staff managed to escape to one of the suburbs.

Having thus delivered the knockout blow to the enemy nerve center, the Luftwaffe was able to devote its maximum effort to military targets such as Yugoslav airfields, routes of communication, and troop concentrations, and to the close support of German ground operations.

The VVKJ put up its Belgrade defence interceptors from the six squadrons of the 32nd and 51st Fighter Groups to attack each wave of bombers, although as the day wore on the four squadrons from the 31st and 52nd Fighter Groups, based in central Serbia, also took part. The Messerschmitt 109E, Hurricane Is and Rogozarski IK-3 fighters scored at least twenty "kills" amongst the attacking bombers and their escorting fighters on 6 April and a further dozen shot down on 7 April. The desperate defence by the VVKJ over Belgrade cost it some 20 fighters shot down and 15 damaged.

Three-pronged drive on the Yugoslav capital
The British, Greek and Yugoslav high commands intended to use Niš as the lynch-pin in their attempts to wear down German forces in the Balkans and it is for this reason that the locality was important. When the Germans broke through in this sector – a sector which was essential if stability was to be maintained on the front – The Yugoslav Supreme Command committed numerous forces from its strategic reserves, including the 2nd Cavalry Division, but these were harassed by the Luftwaffe during transit to the front and did not get through in any real quantities.

Having reached Niš from its initial attacks from Bulgaria and broken the Yugoslav defences, the German 14th Motorised Corps headed north in the direction of Belgrade. The German 46th Panzer Corps had advanced across the Slavonian plain from Austria to attack Belgrade from the west, whilst the 41st Panzer Corps threatened the city from the north after launching its offensive drive from Romania and Hungary. By 11 April, Yugoslavia was criss-crossed by German armoured columns and the only resistance that remained was a large nucleus of the Yugoslav Army around the capital. After a day of heavy fighting German armoured forces broke through these Yugoslav defences and Belgrade was occupied on the night of 12 April.

Hungarian offensive
On 12 April the Hungarian Third Army crossed the border with one cavalry, two motorized and six infantry brigades. The Third Army faced the Yugoslavian First Army. By the time the Hungarians crossed the border, the Germans had been attacking Yugoslavia for over a week. As a result, the Yugoslavian forces confronting them put up little resistance, except for the units in the frontier fortifications, who had held up the Hungarian advance for some time. and inflicted some 350 casualties. Units of the Hungarian Third Army advanced into southern Baranja, located between the rivers Danube and Drava, and occupied the Bačka region in Vojvodina with Hungarian relative majority. The Hungarian forces occupied only those territories which were part of Hungary before the Treaty of Trianon.

Yugoslav Albanian offensive
In accordance with the Yugoslav Army's war plan, R-41, a strategy was formulated that, in the face of a massive Axis attack, a retreat on all fronts except in the south be performed. Here the 3rd Yugoslav Army, in cooperation with the Greek Army, was to launch an offensive against the Italian forces in Albania. This was in order to secure space to enable the withdrawal of the main Yugoslav Army to the south. This would be via Albanian territory in order to reach Greece and the Allied forces to be based there. The strategy was based on the premise that the Yugoslav Army would, together with the Greek and British Armies, form a new version of the Salonika Front of World War I.

On 8 April the hard-pressed VVKJ sent a squadron of fourteen Breguet 19 light bombers to the city of Florina in northern Greece to provide assistance to both the Yugoslav and Greek Armies on the Macedonian front. The squadron performed numerous bombing and strafing missions during the course of the campaign.

The 3rd Yugoslav Army of the 3rd Army Group was tasked with conducting offensive operations against the Italian 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:
 * 15th Infantry Division "Zetska"
 * 13th Infantry Division "Hercegovacka"
 * 31st Infantry Division "Kosovska"
 * 25th Infantry Division "Vardarska"
 * "Komski" cavalry Odred.

The strategic reserve of the 3rd Army Group, the 22nd Infantry Division "Ibarska", was situated around Uroševac in the Kosovo region.

In addition, offensive operations against the Italian enclave of Zara (Zadar) on the Dalmatian coast were to be undertaken by the 12th Infantry Division "Jadranska".

The first elements of the 3rd Army launched their offensive operations in North Albania on 7 April 1941, with the Komski Odred covering the Gusinje-Prokletije mountains area advancing towards the village of Raja-Puka. The Kosovska Division crossed the border in the Prizren area of Kosovo and was advancing through the Drin River valley. The Vardarska Division gained some local success at Debar, while the rest of the army's units were still assembling.

The next day, the 8th, found the Zetska Division steadily advancing along the Podgorica–Shkodër road. The Komski cavalry Odred successfully crossed the dangerous Prokletije mountains and reached the village of Koljegcava in the Valjbone River Valley. South of them the Kosovska Division broke through the Italian defences in the Drin River Valley, but due to the fall of Skopje to the attacks by the German Army, the Vardarska Division was forced to stop its operations in Albania.

The 9 April 1941 saw little further progress for the Yugoslavs, because although the Zetska Division continued advancing towards Shkodër and the Komski Odred reached the Drin River, the Kosovska Division had to halt all combat activities on the Albanian Front due to the appearance of German troops in Prizren. On 10 April 1941 the Zetska Division was still steadily fighting its way towards Shkodër and had advanced 50 km in some places. These advances had been supported by aircraft of the VVKJ's 66th and 81st Bomber Groups, who attacked airfields and Italian troop concentrations around Shkodër, as well as the port of Durrës.

The Komski Odred and the right column of the Kosovska Division advanced along the right bank of the Drin River towards Shkodër in order to link with Zetska Division, but the central and left column of the Kosovska Division were forced to take a defensive perimeter to hold off the increasing pressure by German troops.

Between 11–13 April 1941, with German and Italian troops advancing on its rear areas, the Zetska Division was forced to retreat back to the Pronisat River by the Italian 131st Centauro Armoured Division, where it remained until the end of the campaign on 16 April. The Centauro Division then advanced upon the Yugoslav fleet base of Kotor in Montenegro, also occupying Cettinje and Podgorica.

Local uprisings
At the local level infighting by Yugoslav citizens started even prior to the arrival of Axis troops. Croats in the 108th Infantry Regiment of the 40th Infantry Division "Slavonska" rebelled on the evening of 7–8 April near Grubišno Polje, taking command of the regiment from its Serb officers. They were subsequently joined by the 40th Auxiliary Regiment and elements of the 42nd Infantry Regiment (also from the "Slavonska" Division). With the deteriorating situation in the area, the Yugoslav 4th Army's headquarters was moved from Bjelovar to Popovača. The rebelling regiments then entered Bjelovar, with the city's mayor Julije Makanec proclaiming an Independent State of Croatia on 8 April. Vladko Maček and ban Ivan Šubašić sent messages to the city urging the regiments to maintain their positions, but this was disobeyed by the rebelling military and civil officials who waited for the arrival of the German army.

10 April saw clashes between Ustaša supporters and Yugoslav troops in Mostar. The former taking control of the city. Several VVKJ aircraft were damaged and disabled on Jasenica airfield near Mostar, including several Dornier Do-17Ks and Savoia Marchetti SM-79 K bombers.

On 11 April domestic Ustaša agents took power in Čapljina. They intercepted Yugoslav troops headed by rail from Mostar to Trebinje and disarmed them. A backup Yugoslav force from Bileća was sent in which retook the town on 14 April, before the arrival of the Germans in the coming days.

Naval operations
When Germany and Italy attacked Yugoslavia on 6 April 1941, The Yugoslav Royal Navy had available three destroyers, two submarines and 10 MTBs as the most effective units of the fleet. One other destroyer, the Ljubljana was in dry-dock at the time of the invasion and she and her anti-aircraft 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 was close to the Albanian border and the Italo-Greek front there, but Zara (Zadar), an Italian enclave, was to the north-west of the coast and to prevent a bridgehead being established, the destroyer Beograd, four of the old torpedo boats and 6 MTBs were despatched to Šibenik, 80 km to the south of Zara, in preparation for an attack. The attack was to be co-ordinated with the 12th "Jadranska" Infantry Division and two "Odred" (combined regiments) of the Yugoslav Army attacking from the Benkovac area, supported by air attacks by the 81st Bomber Group of the VVKJ. The Yugoslav forces launched their attack on 9 April but by 13 April the Italian forces had counter-attacked 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 Šibenik when her starboard engine was put out of action, after which she limped to Kotor, escorted by the remainder of the force, for repair. The maritime patrol float-planes of the VVKJ flew reconnaissance and attack missions during the campaign, as well as providing air cover for mine-laying operations off Zara (Zadar). Some of their successes included an Italian tanker being damaged by a near miss off the Italian coast near Bari, attacks on the Albanian port of Durrës, as well as strikes against Italian re-supply convoys to Albania. On 9 April, one Dornier Do 22K floatplane notably took on an Italian convoy of 12 steamers with an escort of eight destroyers crossing the Adriatic during the day, attacking single-handed in the face of intense AA fire.

The Royal Yugoslav Navy also had at its disposal four large, heavily armed and armoured river monitors in its riverine flotilla. They were used to patrol the Danube, Drava and Sava rivers in the northern parts of Yugoslavia and its border with Hungary. These monitors, the Drava, Sava, Morava and Vardar had been inherited from the Austrian Navy at the end of World War I. All were of around 400-500t with a main armament of two 120 mm guns, two or three 66 mm guns, 120 mm mortars, 40 mm AA guns and machine guns. At the start of the campaign they had carried out 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 German Ju 87 dive-bombers attacked the Yugoslav monitors on the Danube. The Drava, commanded by Aleksandar Berić, was hit by several of them but they were unable to penetrate the Drava's 300 mm thick deck armour, until, by chance, one put a bomb 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 the bases and the river systems upon which they operated.

Losses
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 Panzer Corps 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 Italian Army took heavy casualties in northern Albania from the Yugoslav offensive there, whilst the Italian Air Force lost approximately 10 aircraft shot down, with a further 22 damaged. 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 a Hungarian parachute 'battalion' becoming casualties when a transport aircraft filled with 30 troops went down during an abortive drop on 12 April. The Hungarians also lost five Fiat fighters and one Weiss WM-21 Sólyom reconnaissance aircraft during the fighting.

The Germans took between 254,000 and 345,000 Yugoslav prisoners (excluding a considerable number of ethnic Croats, Germans and Hungarians who had been conscripted into the Yugoslav Army and who were quickly released after screening) and the Italians took 30,000 more.

Approximately 1,000 army and several hundred VVKJ personnel (including one mobile-workshop unit of six vehicles) escaped via Greece to Egypt.

In their brief fight, the VVKJ suffered the loss of 49 aircraft to Axis fighters and anti-aircraft fire, with many more damaged beyond repair. These losses had cost the lives of 27 fighter pilots and 76 bomber aircrew. 85 more aircraft had been destroyed on the ground by air attack, while many others had been destroyed or disabled by their own crews, or had crashed during operations, or in 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, with four making it 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 on to the newly created Air Force of the Independent State of Croatia, Finland, Romania and Bulgaria.

The Italians captured most of the Yugoslav Navy (one of its four destroyers, the Ljubljana, had spent the campaign in dry-dock). However, another destroyer, the Zagreb, was blown up at Kotor by two of its officers to prevent capture and one of the British-built submarines and two MTBs succeeded in escaping to Alexandria in Egypt to continue to serve with the Allied cause. It should also be noted that a fourth destroyer was captured while under construction in the Kotor shipyard, the Split, but the Regia Marina was not able to finish her before the armistice in 1943. Eventually, she was recovered after the war by the Yugoslavians and completed under the original name. Ten Yugoslav Navy maritime patrol float-planes escaped to Greece, with nine making it to Egypt, where they formed a squadron under RAF command.

Armistice and surrender
The Axis victory was swift. As early as 14 April the Yugoslav high command had decided to seek an armistice and authorised the army and army group commanders to negotiate local ceasefires. That day the commanders of the 2nd and 5th Armies asked the Germans for terms, but were rejected. Only unconditional surrender could form the basis for negotiations they were told. That evening, the high command sent an emissary to the headquarters of Panzer Group Kleist to ask for armistice, and in response General von Kleist sent the commander of the 2nd Army, von Weichs, 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 did not have authority to sign the document, he was given a draft of the agreement and an aircraft was placed at his disposal to bring in authorised representatives of the government. Finally, on 17 April, after only eleven days of fighting, the pre-coup Foreign Minister Aleksandar Cincar-Marković and General Milojko Janković signed the armistice and unconditionally surrendered all Yugoslav troops. It came into effect the follow day (18 April) at noon. At the signing, the Hungarians and Bulgarians were represented by liaison officers, but they did not sign the document because their countries were not at war with Yugoslavia. The Italian representative, Colonel Luigi Buonofati, signed the document after noting that "the same terms are valid for the Italian army".

The insistence of the Yugoslav Army on trying to defend all the borders assured their failure from the start. After the surrender, Yugoslavia was subsequently divided amongst Germany, Hungary, Italy and Bulgaria, with most of Serbia being occupied by Germany. The Italian-backed Croatian fascist leader Ante Pavelić declared an Independent State of Croatia before the invasion was even over.

Beginning with the uprising in Serbia in July 1941, there was continuous resistance to the occupying armies in Yugoslavia, mainly by the Partisans and to a lesser extent by the Chetniks, until the end of the war.

Books

 * Geschichte des Zweiten Weltkrieges Vol. 3, A. A. Gretschko, Berlin: Militärverlag der Deutschen Demokratischen Republik, 1977.
 * Niehorster, Leo W.G. The Royal Hungarian Army, 1920–1945, Europa Books Bayside New York 1998 ISBN 978-1-891227-19-6
 * The Times Atlas of the Second World War, John Keegan (ed.), New York: Harper and Row, 1989.
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Geschichte des Zweiten Weltkrieges Vol. 3, A. A. Gretschko, Berlin: Militärverlag der Deutschen Demokratischen Republik, 1977.
 * Niehorster, Leo W.G. The Royal Hungarian Army, 1920–1945, Europa Books Bayside New York 1998 ISBN 978-1-891227-19-6
 * The Times Atlas of the Second World War, John Keegan (ed.), New York: Harper and Row, 1989.
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Niehorster, Leo W.G. The Royal Hungarian Army, 1920–1945, Europa Books Bayside New York 1998 ISBN 978-1-891227-19-6
 * The Times Atlas of the Second World War, John Keegan (ed.), New York: Harper and Row, 1989.
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * The Times Atlas of the Second World War, John Keegan (ed.), New York: Harper and Row, 1989.
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * The Times Atlas of the Second World War, John Keegan (ed.), New York: Harper and Row, 1989.
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7
 * Whitely, M.J., Destroyers of World War Two: An International Encyclopedia, US Naval Institute Press, 2001. ISBN 978-0-87021-326-7