Operation Retribution ( 1941 ) Operation Retribution ( ) also known as Operation Punishment , was the codename used for the German bombing of Belgrade , the capital of the Kingdom of Yugoslavia , in April 1941 . The operation commenced on 6 April and concluded on 10 April , resulting in paralysis of Yugoslav civilian and military command and control , widespread destruction largely in the centre of the city , and significant civilian casualties . The bombing of Belgrade was combined with air attacks on a large number of Royal Yugoslav Air Force airfields and other strategic targets across Yugoslavia . The commencement of the bombing coincided with the German - led Axis invasion of Yugoslavia , which resulted in the surrender of Yugoslav forces on 17 April . Background . After the 1938 " Anschluss " ( union ) of Germany with Austria , Yugoslavia shared a border with Germany and came under increasing pressure as her neighbours fell into line with the Axis . In April 1939 , Yugoslavia gained a second frontier with Italy when that country invaded Albania . Between September and November 1940 , Hungary joined the Tripartite Pact , Italy invaded Greece , and Romania also joined the Pact . From that time , Yugoslavia was almost surrounded by Axis powers or their satellites , and her neutral stance toward the war was under tremendous pressure . On 14 February 1941 , Adolf Hitler invited the Yugoslav Prime Minister Dragiša Cvetković and his foreign minister Aleksandar Cincar - Marković to Berchtesgaden and requested that Yugoslavia also join the Pact . Two weeks later , Bulgaria joined the Pact . The next day , German troops entered Bulgaria from Romania , closing the ring around Yugoslavia . Further pressure was applied by Hitler on 4 March 1941 , when the Yugoslav Regent , Prince Paul , visited Berchtesgaden , but Prince Paul delayed a decision . On 7 March , British troops began landing in Greece to bolster the defences of their Balkan ally against the Italians . Hitler , wanting to secure the southern flank of his impending invasion of the Soviet Union , demanded that Yugoslavia sign the Pact , and the Yugoslav government eventually complied on 25 March 1941 . Two days later a military coup d ' état was carried out by a group of Royal Yugoslav Air Force and Yugoslav Royal Guard officers , led by Brigadier General Borivoje Mirković . Prince Paul was deposed and replaced by the 17 - year - old King Peter II who was declared to be of age . On the same day as the Yugoslav coup d ' état , Hitler issued Directive 25 , which stated that the coup had changed the political situation in the Balkans . He ordered that " even if Yugoslavia at first should give declarations of loyalty , she must be considered as a foe and therefore must be destroyed as quickly as possible . " Bombing . Hitler decided that Belgrade would be bombed in " retribution " for the coup against the government that had signed the Pact . In order to carry out Hitler ' s orders , on 27 and 28 March 1941 " Reichsmarschall " Hermann Göring transferred about 500 fighter and bomber aircraft from France and northern Germany . The commander of " Luftflotte IV " , " Generaloberst " ( General ) Alexander Löhr , allocated these aircraft to attack the Yugoslav capital in waves by day and night . Löhr issued his orders for the bombing on 31 March , but the decision to bomb Belgrade was not confirmed by Hitler until 5 April . Although Hitler ordered the general destruction of Belgrade , Löhr replaced these general directions with specific military objectives at the last minute . On 6 April 1941 , a massive air attack was unleashed on Belgrade and every airfield and installation of the Royal Yugoslav Air Force , without a declaration of war . Bombers and dive - bombers dropped of bombs and incendiaries on the capital . The " Luftwaffe " units involved were commanded by " Fliegerkorps VIII " and included " Kampfgeschwader " ( bomber wings ) 2 , 4 and 51 , and " Sturzkampfgeschwader " ( dive bomber wing ) 77 , with protection provided by the " Jagdgeschwader " 54 fighter wing . The first wave of the assault , consisting of between 150 and 234 bombers and dive - bombers escorted by 120 fighter aircraft , descended on Belgrade at 07 : 00 . In response , the Royal Yugoslav Air Force scrambled 20 Messerschmitt Bf 109 s , 18 Hawker Hurricane s and six locally manufactured Rogožarski IK - 3 fighter aircraft . Some Yugoslav Hurricane pilots engaged friendly Bf 109s as well as attacking " Luftwaffe " aircraft . About 50 Yugoslav aircraft were destroyed by the first wave of strikes . Later that day , three additional waves of German aircraft hit Belgrade , each consisting of about 100 aircraft . Bombing continued on 7 April . The weak Royal Yugoslav Air Force and inadequate anti - aircraft defences of Belgrade briefly attempted to meet the overwhelming " Luftwaffe " assault , but were eliminated as threats during the first wave of the attack . Sources vary regarding the success achieved by the defenders . A U . S . Army study first published in 1953 states that the " Luftwaffe " lost two fighter aircraft , and shot down 20 Yugoslav aircraft and destroyed 44 on the ground , whereas other sources state that the Yugoslavs shot down 40 German aircraft over the two - day air battle . Dive - bombers in subsequent waves were able to operate at rooftop altitude . According to the historian Professor Stevan K . Pavlowitch , the bombing of Belgrade lasted for three days , other sources state the air battle over Belgrade lasted just two days owing to poor flying weather on 8 April . The most important cultural institution that was destroyed was the National Library of Serbia , which was hit by bombs and gutted by fire . Hundreds of thousands of volumes , rare books , maps , and medieval manuscripts were destroyed . British retaliation . No . 37 Squadron of the Royal Air Force conducted two bombing raids on Sofia , the capital of Bulgaria , in retaliation for the bombing of Belgrade . Operating Vickers Wellington bombers flying from an airfield in Greece , the squadron conducted raids on 6 – 7 April and 12 – 13 April , dropping a total of of high - explosive bombs on railway targets and nearby residential areas . These raids were carried out despite the fact that Britain was not at war with Bulgaria until 12 December 1941 . Aftermath . The bombing of Belgrade paralysed communications between the Yugoslav military and its headquarters , and contributed decisively to the rapid collapse of Yugoslav resistance . Civilian casualties were significant , but sources vary widely from 1 , 500 to 17 , 000 killed . According to the journalist William Stevenson , around 24 , 000 corpses were recovered from the ruins , and many were never found . The official casualty figure soon after the bombing was 2 , 271 killed , but other sources use 5 , 000 or 10 , 000 , with later Yugoslav estimates ranging even higher . In contrast , Professor Jozo Tomasevich states that the higher estimates were downgraded following " careful postwar investigations " , and indicates that a figure between 3 , 000 and 4 , 000 is more realistic . Following the Yugoslav capitulation , " Luftwaffe " engineers conducted a bomb damage assessment in Belgrade . The report stated that of bombs were dropped , with 10 – 14 percent being incendiaries . It listed all the targets of the bombing , which included : the royal palace , the war ministry , military headquarters , the central post office , the telegraph office , passenger and goods railway stations , power stations and barracks . It also mentioned that seven aerial mines were dropped , and that areas in the centre and northwest of the city had been destroyed , comprising 20 – 25 percent of its total area . Some aspects of the bombing remain unexplained , particularly the use of the aerial mines . In contrast to this report , Pavlowitch states that almost 50 percent of housing in Belgrade was destroyed . After the invasion , the Germans forced 3 , 500 to 4 , 000 Jews to collect rubble that was caused by the bombing . Löhr was captured by the Yugoslav Partisans on 9 May 1945 , escaped , and was recaptured on 13 May . He was intensively interrogated , after which he was tried before a Yugoslav military court on a number of war crimes charges , one of which related to his command of " Luftflotte IV " during Operation Retribution . He was convicted , sentenced to death and executed .