On 6th April 1941., Axis forces attacked the Kingdom of Yugoslavia as well as Greece. Direct cause of the attack was the military coup of 27th March which overthrew the Cvetković – Maček government and installed king Peter, a minor son of king Alexander. Invasion was, despite expectations of both sides, rather anticlimactic – Yugoslavia capitulated after only 12 days. For comparison, Poland defended itself from 1st September until 26th September.
While Yugoslav Army was a good force for the war it was designed to fight, that war was a trench war against a World War I army – not a mobile war against a mechanized opponent like German Wehrmacht. And there were even worse aspects.
Yugoslav Royal Army did have a war plan against invasion – plan R-41. But that plan was changed and modified by Yugoslav politicians according to their current political requirements. Even if it was not, the plan was based on the plans of the French Army – same army that Germany overran in six weeks.
During 1920s and 1930s the Yugoslav war plans were based on stopping the attacker in a frontal confrontation before shifting momentum with a series of minor counterattacks. Artillery would be used to provide fire support. In case of a larger attack, idea was to delay the enemy before withdrawing into Bosnian mountains.
But then politicians got involved, and so a new plan was made.
This plan was essentially a replay of the First World War. Plans predicted that some 27 divisions – 85% of the total strength of the Yugoslav Army – would be deployed along the border. The idea was to defend the border and buy time for the army to withdraw in Greece where it would join the Allied forces. In order to delay the enemy, army would set up several fixed lines of defense.
As it was, the new plan would likely not manage to stop even the Austro-Hungarian army, let alone modern army such as Wehrmacht. But bad news did not stop there.
Kingdom of Yugoslavia was closely allied with France. Yugoslav Army was essentially a pale imitation of the French army: uniforms, helmets, equipment… Yugoslav government even bought a large number of obsolete French tanks. Yugoslav officers were also being sent on education in France, where they were taught outdated French defensive doctrine based around the First World War. Antitank artillery consisted of 20 mm to 47 mm guns, all of which were completely useless against German tanks. Lack of armored transports and other vehicles meant that the army could march at speeds of 20 kilometers per day at most, much of its logistics still being mule-drawn. All of the 110 tanks Yugoslavia had were obsolete. The only good part of the Yugoslav Army was the Air Force, which had 300 modern combat aircraft. These were stationed in 23 air bases, and while majority had been destroyed on the ground, Air Force still managed to offer stiff resistance before being neutralized by Axis ground advance. Yugoslavia could mobilize 1 200 000 soldiers and 500 000 reservists, but could not supply them as weak industry meant that it was heavily dependant on imports for its supply of ammunition. Infantry units had ammunition for 75 days of combat, artillery for 100 days, and antitank guns had 75 projectiles per cannon.
Kingdom of Yugoslavia also exchanged with France all of the intelligence documents and war plans.
When Germany overran France, French defenses collapsed. There was no time for many of the sensitive materials to be destroyed. And in one of the railway cars, Germans found Yugoslav defense plans – which were not even coded.
When Yugoslavia was attacked a year later, Germans used these plans. Yugoslav authorities had been aware of German possession of their plans – and did nothing. So when Germany and her allies attacked Yugoslavia on 6th of April, all the defenses immediately collapsed and Yugoslav war plans went up in smoke. Worse, Yugoslavia never declared full mobilization, and partial mobilization had been declared only three days before the start of the war. While Yugoslav Army had 33 divisions on paper, they were not fully mobilized. Of these, 27 were placed on the border and another four as High Command’s own reserve. With little in way of air support or mobile warfare doctrine, these had to stop 60 Axis divisions of which 15 armored, with 500 tanks and 2 200 aircraft (1 500 German). Worse, Yugoslav forces were commanded by generals whose general level of competence was somewhere between General Melchett and Zap Brannigan. Said officers were only taught about frontal attacks, with any form of maneuver warfare – even the simple flanking maneuvers – being higher dimension mathematics for them. It is thus hardly a surprise that the Yugoslav Army fell apart almost immediately.
Axis forces completely surrounded Yugoslavia, with only border towards Greece being friendly ground. Germany had a prepared plan, “Directive No.25”, which predicted concentric attacks from Austria and Bulgaria towards Belgrade, with the aim of destroying Yugoslav Army while preventing its retreat into Greece. 60 Axis divisions surrounded the country. German Second Army with 11 divisions was positioned in Austria and Hungary. 12th Army in Romania and Bulgaria had been reinforced to 19 divisions, of which 8 motorized. Further 5 divisions were in reserve. Germany also had 1560 aircraft. Italy had the Second Army with 14 divisions positioned towards Slovenia and Croatia. One division was in Zadar, and eight in Albania (remaining 22 division in Albania being oriented towards Greece). Italy had also prepared 670 aircraft. Hungary had five divisions.
Luftwaffe bombarded Belgrade on the very first day, three times in a row, killing 7 000 people. This was done despite Yugoslav government having declared Belgrade an “open city”. Also bombarded were Zagreb, Banja Luka and other cities forming important communication hubs. Particular target were the air fields, but also other major targets – which Germans had precise information on. It is thus not surprising that Germans managed to destroy 64 aircraft on the ground.
Next day, on Monday, 7th April, Skopje fell to strong attacks of German forces from Bulgaria. Southern border was now cut off, which is precisely what Germans had been aiming for, being aware of Yugoslav plans to retreat into Greece. But retreat to Greece was in any case impossible as Greece was also being attacked. In short, Yugoslav war plan was rendered void after only the first day of the invasion. Worse, political pressure meant that the army was positioned to defend the border along its entire length. And to top it off, because of decades of forcible centralization and tyranny, only a fraction of the army was actually interested in defending the country (contrast with Austria-Hungary, where army actually survived the Empire it was defending).
On 8th April, German forces invading from Bulgaria reached Niš, and took Zaječar in the early morning. In the West, entirety of Slovenia had fallen and Germans crossed Drava near Varaždin. There was no resistance: nobody was willing to die for the Kingdom, with minor fighting happening only near Karlovac, but Germans soon linked up with Italians there.
By 9th April the entirety of Croatian Zagorje had been secured. German forces also captured Niš. Slovenes and Croatians are massively escaping the Yugoslav (really Serbian) army.
By 10th April the entirety of Macedonia had fallen to the invader. German forces entered Zagreb, where they were welcomed as liberators. Similar welcome was organized also in other Croatian cities and villages. By this time the Yugoslav Third (Macedonia) and Fourth (Croatia) Army had ceased to exist. Serbia was still defended by the Fifth Army, but this army had been partially encircled east of the river Velika Morava. Elements of the First and Second Armies were in full retreat from Baranja and Bačka. Only the Third Army had mounted a successful offensive against Italian forces in Albania.
By 11th April Germans are already in Virovitica, Slatina, Požega, Slavonski Brod, Osijek, Đakovo, Vikovci. They soon reached Danube in Vukovar, Županja and Ilok. In Đakovo, local population led by Volksdeutchers – who were living there in large numbers before partisans ethnically cleansed them in 1945. – greeted the German army with food and cakes prepared for the Easter of that year (13th April 1941). In Bosnia, there was no fighting at all. There was some resistance in Serbia, but even that is very weak.
On 12th April a German platoon from the 2nd Waffen SS Division “Das Reich” captured Belgrade and its 1 350 defenders. Yugoslav government, ministers, military leaderships and the royal family fled the country, taking all the gold while leaving several million paper banknotes that were worth absolutely nothing.
On 14th April, High Command requested ceasefire from Germans, but they refused, requiring instead an unconditional surrender.
By 15th April all the combat operations were over and the remnants of the Yugoslav Army were surrendering.
On 16th April entirety of Yugoslav High Command was captured near Sarajevo.
Unconditional surrender was signed on 17th April, coming into effect on midnight of 17th onto 18th April.
Quick end of the war had surprised everybody, Germans included. Their pre-war estimates expected the campaign to only be finished in early May, yet Yugoslavia had fallen in 11 days. Casualties were absolutely minor: Germans had lost only 152 dead, 392 wounded and 15 disappeared, which sharply contrasted pre-war estimates of 10 000 casualties.
Serbian propaganda ascribed quick collapse to Slovene and Croatian treason. While this was a complete nonsense, it helped fuel many crimes later on. Nearly 700 000 people will die in the next years on the area of the former, unnecessary and unfortunate kingdom. One has to consider whether the Second World War will have happened at all had Austria-Hungary survived.
History and War 
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