German bombing of Belgrade

• 1. Introduction

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  On the 6th of April 1941, the skies above Belgrade turned dark. Not from clouds, but from the engines of hundreds of German aircraft converging on the Yugoslav capital in what Hitler himself had ordered as punishment for a coup that had overthrown a compliant government just days earlier. The operation even carried the word for punishment in its name: Unternehmen Strafgericht, which translates roughly as Operation Retribution. By nightfall, between 20 and 25 per cent of Belgrade's total area lay destroyed. The water and electrical systems had been gutted. The National Library of Serbia had burned to the ground. And the number of civilians killed would be disputed for decades.

  How did a city go from declared neutral to bombed rubble in a matter of days? Why did Hitler decide to destroy a capital that had, just weeks earlier, been a potential ally? And what became of the men who ordered those bombs dropped, and the man who betrayed his own country's defences from the inside? Those are the questions this documentary follows.

• 2. The Pact and the Coup

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  Adolf Hitler's interest in Yugoslavia sharpened considerably after Germany's 1938 annexation of Austria, which gave the two countries a shared border for the first time. Pressure mounted steadily as Yugoslavia watched its neighbours fall into line with the Axis. Hungary, Romania, and Bulgaria all joined the Tripartite Pact between September and November 1940, and by early 1941 Yugoslavia was nearly encircled by Axis powers or states aligned with them.

  On the 14th of February 1941, Hitler summoned Yugoslav Prime Minister Dragiša Cvetković and Foreign Minister Aleksandar Cincar-Marković to his retreat at Berchtesgaden and pressed them to join the Pact. Four days before the formal signing, Hitler pushed harder when Prince Paul, the Yugoslav regent, made his own visit to Berchtesgaden on the 4th of March. The prince stalled. On the 25th of March, the Yugoslav government finally complied and signed.

  Two days later, everything changed. A group of officers from the Royal Yugoslav Army Air Force and the Royal Guard, led by Brigadier General Borivoje Mirković, launched a coup d'état. They deposed Prince Paul and placed his 17-year-old nephew Peter on the throne as king. The signing of the Pact was effectively undone.

  Hitler's reaction was immediate. On the very day of the coup, he issued Directive 25, declaring that Yugoslavia must be "destroyed as quickly as possible", even if the new government offered declarations of loyalty. Within two days, Reichsmarschall Hermann Göring had transferred approximately 500 fighter and bomber aircraft from France and northern Germany to airfields near the Yugoslav border.

• 3. The Defector and the Warning

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  On the 3rd of April 1941, Major Vladimir Kren of the Royal Yugoslav Army Air Force climbed into a Potez 25 aircraft at Zemun and flew it to Graz, where he surrendered to the Germans. What he carried with him proved devastating. Kren disclosed the locations of Yugoslavia's dispersal airfields, the codes used by the Yugoslav air force, the positions of troop mobilisation centres, and the locations of air-raid shelters in Belgrade itself.

  The codes had to be changed immediately. But the shelter locations were already in German hands, and thousands of civilians who would seek refuge there during the bombing were now dangerously exposed.

  On the afternoon of the 5th of April, a British colonel arrived at the VVKJ base in Zemun and met with Mirković, the same officer who had led the coup. The colonel informed him that the German attack on Belgrade would begin at 06:30 the following morning. The Yugoslav government had already declared Belgrade an open city the previous day, a status intended under international convention to spare it from bombardment. The German embassy had confirmed to Berlin that Belgrade contained no anti-aircraft defences. Despite this, German propaganda, after the first bombs had fallen, labelled the city "Fortress Belgrade" to justify the attack to its own public.

  Generaloberst Alexander Löhr, commanding Luftflotte IV, had issued his orders for the bombing on the 31st of March. Hitler himself did not confirm the decision until the 5th of April. At the last minute, Löhr replaced Hitler's general order to destroy Belgrade with a specific list of military objectives within the city.

• 4. Four Waves Over Belgrade

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  German ground forces crossed the Yugoslav border at 05:15 on the 6th of April. At 06:00, the Reich Minister of Propaganda Joseph Goebbels announced Germany's declaration of war. The Yugoslav capital had roughly thirty minutes before the first bombs fell.

  The first wave closed in between 06:30 and 06:45. It consisted of 74 Junkers Ju 87 Stuka dive bombers, along with 160 Heinkel He 111 medium bombers and Dornier Do 17 light bombers flying at between 8,000 and 10,000 feet. Above them flew Messerschmitt Bf 110 heavy fighters at 11,000-12,000 feet and 100 Messerschmitt Bf 109E fighters at 15,000 feet. The entire Yugoslav 6th Fighter Brigade, mustering 29 Messerschmitt Bf 109Es and five Rogožarski IK-3s, scrambled to intercept. They were met almost immediately by escorting Bf 109Es from Jagdgeschwader 77. The defending Hawker Hurricane Mk1s of the 52nd Fighter Group arrived just as the first wave was departing and claimed one Stuka shot down. Immediately after the first wave, King Peter, the Yugoslav government, and the Supreme Command left Belgrade and retreated into the country's mountainous interior.

  The second wave arrived around 10:00, consisting of 57 Ju 87 dive bombers and 30 Bf 109E fighters. The third wave struck at 14:00, with 94 twin-engined bombers from airfields near Vienna escorted by 60 fighters. The fourth attack came at 16:00, comprising 97 dive bombers and 60 fighters. By the end of the first day, Yugoslav losses totalled ten aircraft shot down and fifteen damaged; the Germans lost twelve aircraft, significantly fewer than the Yugoslavs claimed.

  One Luftwaffe pilot who recorded his first aerial victory over Belgrade that day was Oberleutnant Gerhard Koall of Jagdgeschwader 54. He went on to be credited with 37 victories and received the Knight's Cross of the Iron Cross in 1944. Attacks continued in subsequent days, though poor flying conditions on the 8th of April limited operations.

• 5. What the Bombs Destroyed

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  The first wave alone hit the Belgrade power station, the post office and its telegraph services, the headquarters of the Ministry of Army and Navy, the Yugoslav Supreme Command building, the military academy, the royal palace at Dedinje, the royal guard barracks at Topčider, and the airport at Zemun. With each successive wave, the city's capacity to function or resist collapsed further. Dive-bombers in later waves were able to operate at rooftop altitude, a sign of how thoroughly the defences had been neutralised.

  The toll on civilian Belgrade reached well beyond the military and government infrastructure. The most significant cultural loss was the National Library of Serbia, which bombs struck and fire then consumed entirely. Hundreds of thousands of rare books, maps, and medieval manuscripts were reduced to ash. The Belgrade Zoo was also hit, and frightened animals ran through the streets of a city already in chaos.

  German Luftwaffe engineers who later assessed the damage reported that 218.5 metric tonnes of bombs had been dropped, with 10 to 14 per cent being incendiaries. Seven aerial mines were also deployed, a fact that historians have found difficult to fully explain. Areas in the centre and north-west of Belgrade were destroyed, accounting for between 20 and 25 per cent of the city's total area. The historian Stevan K. Pavlowitch estimates that nearly 50 per cent of Belgrade's housing was destroyed.

  Civilian deaths remain disputed. The occupation authorities reported 2,271 killed shortly after the attack. Other estimates have placed the figure between 5,000 and 10,000. The historian Jozo Tomasevich concluded after reviewing the evidence that a figure in the range of 3,000 to 4,000 is more realistic, the higher Yugoslav estimates having been reduced by careful postwar investigation. After the invasion, the Germans forced between 3,500 and 4,000 Jews to clear the rubble left by the bombardment.

• 6. Accountability and Memory

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  Alexander Löhr survived the war but not its aftermath. Yugoslav Partisans captured him on the 9th of May 1945. He escaped, was recaptured on the 13th of May, and underwent intensive interrogation. A Yugoslav military court tried him on multiple war crimes charges, including his command of Luftflotte IV during Operation Retribution. He was convicted and executed on the 26th of February 1947.

  Vladimir Kren's fate followed a parallel arc. After his defection he was appointed head of the Air Force of the Independent State of Croatia, the German-backed puppet state established after Yugoslavia's collapse. He was arrested in Italy in March 1947, not for his defection itself, but on separate charges of war crimes arising from his role in directing the Croatian air force's attacks on civilians. Yugoslavia sought his extradition, obtained it, tried him, convicted him on all counts, and executed him in 1948.

  The RAF's own retaliation is a lesser-known coda. No. 37 Squadron flew Vickers Wellington bombers from an airfield in Greece and conducted two raids on Sofia, the Bulgarian capital, on the nights of 6/the 7th of April and 12/the 13th of April. The squadron dropped a total of 30 tonnes of high-explosive bombs on railway targets and nearby residential areas. Britain was not formally at war with Bulgaria until the 12th of December 1941, making the legal and moral basis for the raids contested. The historian Herman Knell described the retaliatory justification as "strange and implausible".

  Belgrade itself was occupied on the 13th of April. Four days later Yugoslavia surrendered. A monument to the Yugoslav pilots who died defending the city was inaugurated at Zemun on the 6th of April 1997, the 56th anniversary of the attack, designed by sculptor Miodrag Živković. On the 75th anniversary in 2016, a memorial service was attended by Serbian Minister Aleksandar Vulin. In June 2017, authorities announced that the ruined foundations of the National Library of Serbia would be converted into a memorial garden. Unexploded German bombs continue to be found beneath Belgrade's streets into the 21st century.