'Strafgericht' was the German bombing campaign against Belgrade designed to terrorise the Yugoslav government and people into submission, and also to exact 'retribution' for what Adolf Hitler took to be Yugoslavia’s defection from the Axis cause after the pro-German regency had been overthrown (6/8 April 1941).

The operation was undertaken within 'Unternehmen 25' by General Alexander Löhr’s Luftflotte IV in support of the land advance on the Yugoslav capital by Generaloberst Maximilian Reichsfreiherr von Weichs’s 2^nd Army and Generalfeldmarschall Wilhelm List’s 12^th Army. Although Hitler had specifically ordered the destruction of the city, his orders were changed by Löhr at the last minute into an attack on communication, military and logistical targets.

After Hitler’s decision that Belgrade was to be bombed as a German 'judgement' on the coup against the government which had signed the Tri-Partite Pact, on 27/28 March Reichsmarschall Hermann Göring ordered the movement of about 500 fighters and bombers from France and northern Germany, and 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.

Germany, Italy and probably Hungary deployed up to 2,000 combat aircraft for operations over Yugoslavia during the period in which Belgrade was bombed. The defensive capability of the Vazduhoplovstvo Vojske Kraljevine Jugoslavije (royal Yugoslav air force) was vested a fighter force most of whose aircraft were obsolete. Out of 487 operational combat aircraft on the strength of the Yugoslav air force in April 1941, fewer than 150 of them effective enough to pose more than a notional threat to modern German fighters.

On 3 April, Major Vladimir Kren of the VVKJ defected to the Germans, flying a Potez 25 aircraft to Graz in annexed Austria, and handed over details of the locations of many of the Yugoslav dispersal airfields and the radio codes used by the VVKJ, which were quickly changed. On the afternoon of 5 April, a British colonel visited Brigadier General Borivoje Mirković, the commander of the VVKJ, at the service’s Zemun base, and confirmed on the basis of British intelligence that the attack on Belgrade would begin at 06.30 on the following morning.

The German ground forces crossed the border into Yugoslavia at 05.15 on 6 April, and the German propaganda minister, Dr Joseph Goebbels, announced the German declaration of war at 06.00. The Yugoslav anti-aircraft defences had raised a false alarm when they reported the approach of an air raid from the direction of Romania at 03.00, but what the listening posts on the Yugoslav/Romanian frontier had actually heard was the engines of the fighters and dive-bombers of Oberleutnant von Schönborn-Wiesentheid’s Romanian-based Fliegerführer Arad command warming up before they started to take off. The VVKJ’s 51^st Fighter Group at Zemun had been on alert before dawn, and when there began to arrive reports of German air attacks on VVKJ airfields, the first patrol was sent into the air. At this earlier stage, however, no warplanes could be seen on their way toward Belgrade.

Taking off from bases in Romania, the first wave of German warplanes closed on Belgrade at 06.45 with 74 Junkers Ju 87 Stuka dive-bombers and 160 Heinkel He 111 medium bombers and Dornier Do 17 light bombers at altitudes of between 7,875 and 9,845 ft (2400 and 3000 m). The bombers were escorted by Messerschmitt Bf 110 heavy fighters at altitudes of between 11,155 to 12,140 ft (3400 to 3700 m) and 100 Messerschmitt Bf 109E fighters at an altitude of 15,090 ft (4600 m). The whole of the Yugoslav 6^th Fighter Brigade (51^st Fighter Group at Zemun and 32^nd Fighter Group at Prnjavor), totalling 29 Bf 109E and five Rogozarski IK-3 single-seat fighters, was scrambled to effect an interception. The Yugoslav fighters were swiftly engaged by the Bf 109E fighters of Major Bernhard Woldenga’s Jagdgeschwader 77. Just as the first wave was departing, Hawker Hurricane Mk I fighters of the 52^nd Group of the Knić-based 2^nd Fighter Brigade arrived over Belgrade and engaged some of the dive-bombers, claiming one Ju 87 shot down.

During this first-wave attack, the Yugoslavs claimed 15 German aircraft shot down for the loss of five of their own aircraft, and more than six others badly damaged. The pilots of JG 77 claimed 10 Yugoslav aircraft shot down and another six destroyed on the ground. On his return to base, the 51^st Fighter Group’s commander was relieved of his command for failure to engage in the action over the Yugoslav capital.

The second wave of German attackers arrived over Belgrade at about 10.00, and comprised 57 Ju 87 dive-bombers and 30 Bf 109E fighters. These were met by 15 of the fighters remaining to the 6^th Fighter Brigade. This time the Yugoslavs claimed two Ju 87 dive-bombers forced down and one Bf 109E shot down. A patrol of the Kragujevac-based 31^st Fighter Group’s Bf 109E fighters, acting without orders of their commander, followed the Germans as they returned to their bases and claimed two dive-bombers shot down for the loss of both Yugoslav aircraft.

The German made another two attacks on Belgrade during 6 April. The third wave, comprising 94 twin-engined bombers flying from airfields near Vienna and escorted by 60 fighters, started its attack at 14.00, and was engaged by 18 fighters of the 6^th Fighter Regiment, whose pilots claimed to have shot down four German aircraft. The fourth attack of the day neared Belgrade at 16.00, and comprised 97 dive-bombers escorted by 60 fighters.

The German air units attacking Belgrade claimed a total of 19 Yugoslav Bf 109E fighters and four unidentified aircraft destroyed on 6 April, but the actual Yugoslav losses on this first day of the German air offensive were 10 aircraft shot down and 15 damaged. In exchange, the Yugoslavs claimed to have shot down 22 German aircraft and forced two more to land. The Germans in fact lost considerably fewer less aircraft than the Yugoslavs claimed, a total of 12 aircraft in the form of two Do 17Z light bombers, five Bf 110 heavy fighters, four Ju 87 dive-bombers, and one Bf 109E fighter.

On 7 April German bombers and dive-bombers dropped between 215 and 360 tons of bombs and incendiaries on the capital. The weak Yugoslav fighter force and the very limited anti-aircraft defences of Belgrade made a brief attempt to engage the overwhelming German assault, but were taken out of the equation during the first wave of the attack, and the German dive-bombers of subsequent attack waves were able to operate right down to roof-top altitude, with a consequent enhancement in the accuracy of their attacks.

(According to one historian, the bombing of Belgrade lasted for three days, but most sources state that the air battle over Belgrade was fought over only two days as a result of poor flying weather on 8 April.)

The most important cultural institution to be destroyed was the Serb national library, which was hit by bombs and gutted by a fire in which hundreds of thousands of volumes, rare books, maps and mediaeval manuscripts were destroyed.

During this period, No. 37 Squadron of the Royal Air Force flew two bombing raids against Sofia, the capital of Bulgaria, in retaliation for the bombing of Belgrade. Flying Vickers Wellington medium bombers from an airfield in Greece, the squadron conducted raids on 6/7 April and 12/13 April, dropping a total of 30 tons of bombs on railway targets and nearby residential areas. These raids were carried out despite the fact that the UK was not at war with Bulgaria until 12 December 1941.

A Luftwaffe survey 10 days after the attack to assess the results obtained by the 218.5 tons or bombs which had been dropped listed among the targets the royal palace, the ministry of defence, military colleges, the main post office, the telegraph office, railway stations, powerplants and barracks.

The attacks were assessed as having killed 2,271 people as officially registered soon after the event, but in actuality probably somewhat more than this figure: something in the order of 5,000 to 10,000 people were probably killed, though some estimates put the figure as high as 17,000, and thousands of buildings were destroyed.

Started before there had been any declaration of war, the bombing was one of the prosecution’s charges which led to the post-war conviction and execution of Löhr.