BELGRADE AWOKE TO AIR RAID sirens on the early morning of Sunday, April 6, 1941. At 6:50 the first German bombers flew over the capital city of Yugoslavia and began dropping their bombs to signal the start of Operation Strafgericht (“ Punishment” ). The attack’s purpose was to pave the way for the German invasion of Yugoslavia and to punish the residents of Belgrade for overthrowing their pro-Fascist government on March 27. General dissatisfaction over the signing of a pact of alliance with the Axis powers by Yugoslavia’s government had resulted in mass demonstrations in the capital and a coup d’etat by a group of young army officers led by General Dusan Simovic. Adolf Hitler, caught amid preparations to assist Italy’s bogged-down forces in Greece, responded to the coup by invading Yugoslavia as well.
Defending Belgrade was the 6th Fighter Wing of the Royal Yugoslav Air Force (JKRV), especially its 51st Group, based at the Belgrade airport in Zemun. Less than 10 minutes after the alert was sounded, 16 fighters of the 102nd, 161st and 162nd squadrons of the 51st Group took off to intercept the German bombers. Ten Messerschmitt Me-109Es of the 102nd were led by six of the best fighters the Yugoslavs had at the time— their own homebuilt Rogozarski IK-3s.
After taking off, the formation scattered in pairs and intercepted the Germans just as they arrived over Belgrade. Second Lieutenant Dusan Borcic and his wingman, 2nd Lt. Eduard Bamfic, separated over Senjak, one plane heading toward Romania while the second continued toward the old fortress at Kalamegdan. When Borcic reached an altitude of 13,125 feet, 18 Dornier Do-17Zs appeared to the north. Closing on them from the rear, he opened fire with his cannon and two machine guns.The nearest German bomber shook, fell out of formation and exploded on the banks of the Danube River. Borcic’s IK-3 had scored the first victory for a Yugoslav fighter in defense of the nation’s capital.
Borcic continued his flight north, where the sky was black with German bombers coming from Hungary. His IK-3 plunged head-on into the enemy formation, its guns firing short bursts. The reckless maneuver confused the German pilots for a moment, but soon the bombers’ numerous Messerschmitt fighter escorts caught Borcic inside a trap known as the “ devil’s circle.” He tried to escape, but Borcic’s moment of glory was soon over as his crippled IK-3 crashed on Belgrade’s Sarajevska Street. Meanwhile, his wingman, Bamfic, was wounded in a fight above the village of Batajnica. Returning to his base, he was again attacked, but he managed to land safely.
Captain Sava Poljanec, commander of the 161st Squadron, was climbing alone in an IK-3 because his wingman, Sergeant Dusan Vujicic, had been forced to return to base by engine problems. From 4,000 meters Poljanec dived on a German formation he spotted over the village of Kmjaca. When he came close enough, he leveled out and opened fire, banked a little and then fired a short 20mm cannon burst.The left engine of a German bomber erupted in flames; then the aircraft fell into the Pancevacki Rit wetlands. Its crew survived and was taken prisoner.
Suddenly, tracers buzzed by Poljanec’s cockpit as 20 yellow-nosed Me-109Es dived toward him. Poljanec, a flight instructor and one of the three best aerobatic pilots in Yugoslavia at that time, rolled and spun his aircraft, but soon was also caught in a devil’s circle. One German pilot made the mistake of flying in front of the IK-3, and Poljanec fired a burst at him. Glycol vapor trailed from the Me- 109’s fuselage as it dived, banking erratically from one side to another, as if the pilot was dead. With other Germans to his left and right, Poljanec had started his approach to the runway at Zemun when his IK-3 was hit again, by an Me-110 that had been strafing the airfield. Poljanec bailed out of his smoking fighter, and the Me-110 was chased away by Sergeant Sava Vujovic of the 101st Squadron.
As another wave of Germans roared in at 10 a.m., Captain Tbdor Gogic and Sergeant Milisav Semiz attacked a formation of JunkersJu-87B dive bombers and shot one down. In a fierce fight with the escorting Messerschmitts, they soon used up their fuel and ammunition and returned to base.
In the course of that first day, as German bombers attacked Belgrade in four waves Yugoslav fighters took off in pairs or small groups to intercept them. Small groups or single bombers continued to make nuisance raids in the evening. By the end of the day, the Yugoslavs claimed to have shot down at least 35 aircraft over their territory. According to the 6th Wing’s commander, Lt. Col. Bozidar Kostic, 10 of the German aircraft were downed by pilots of the 51st Fighter Group. The Germans themselves recorded the loss of two Do-17s, four Ju-87s, one Me-109 and five Me-110s in combat, as well as a sixth Me-110 that crashed on landing.
The IK-3, the principal Yugoslav-built fighter during that brief but spirited aerial struggle of April 1941, had been the brainchild of three engineers: Ljubomir Ilic , Kosta Sivcev and Slobodan ZrnicZrle. Ilic, who gained his polytechnic diploma in Belgium, had an idea for a new fighter that could replace the Czech-built Avia BH-33E, the mainstay of the JKRV He attended the school of aeronautics in Paris, and in the evenings he listened to lectures at the Sorbonne. In Paris, Ilic met Kosta Sivcev, a pilot and an engineer who was working with the Breguet and Hispano-Suiza aircraft industry companies.
The two friends returned to Yugoslavia in 1931 with definite ideas on what their first design would look like. In 1933, after finishing all their calculations and drawings, and testing a model in the wind tunnel at the Eiffel Institute in Paris, they decided to present their project to the chief of the technical department at head quarters, Colonel Srbobran Stanojevic.
The colonel liked the idea immediately, and after battling with various skeptics for nearly a year, he managed to get permission from the ministry council to build a prototype.The new aircraft was designated IK-01, using the first letters of the manufacturer’s name, the Ikarus company in Zemun. It was a high-wing monoplane with fixed, spatted undercarriage and a fully enclosed cockpit. The plane was powered by an 860-hp Hispano-Suiza 12Y-Crs engine and armed with one 20mm cannon firing through the propeller hub and two 7.9mm machine guns in the front upper fuselage. The prototype flew for the first time on April 24, 1934. In its third flight, the pilot started performing aerobatics that were not authorized for the testing program, and the plane crashed when the fabric covering one part of the wing came apart.
A new prototype, the IK-02, was constructed with its wings covered with duralumin instead of fabric. When it was completed in June 1936, it performed well, with a maximum speed of 270 mph— 9 mph faster than originally planned. Between June 14 and 24, 1937, the IK-02 was tested in 16 mock dogfights with a Hawker Fury Mark I— and won all of them, proving itself not only faster than the Fury but also more agile, and with a better rate of climb.
Nevertheless, there were many who opposed introducing the IK-02 into service, for a variety of reasons. One of the skeptics, Captain Leonid Bajdak, expressed his doubts too loudly and was challenged by Lieutenant Janko Drobnikar to a duel in three categories: a climb to 4,000 meters (13,123 feet), a 140-kilometer (87-mile) race from Belgrade to Novi Sad and back, and a simulated dogfight over Zemun.
On the day of the contest, Bajdak, piloting a Fury, and Drobnikar, flying an IK- 02, roared off the runway at Zemun. The IK-02 won the first round, climbing faster than the Fury. After reaching the agreedupon altitude, the two aircraft set off on their race to Novi Sad, and the IK-02 was the victor in that round as well. Then came the dogfight. Both pilots rolled and spun their aircraft to their respective limits, but when the IK-02 at last caught the Fury in its sights, Captain Bajdak surrendered and admitted that the Yugoslav fighter was indeed superior.
Soon afterward, a batch of 12 IK-2s, as the production aircraft were designated, were built at the Ikarus factory. The first were delivered to the 6th Fighter Wing at Zemun, the rest went to the 4th Fighter Wing in Zagreb. On April 9, 1941, six of the 4th Wing’s IK-2s joined eight Hurricanes in defending the 8th Bomber Wing’s airfield at Rovine, near Banja Luka, against 27 German Me-109Es. One IK-2 and two Hurricanes were shot down, but the Germans lost two Me-109s, and another two were badly damaged. Some of the remaining IK-2s were destroyed by their crews prior to the Yugoslav retreat, while three planes were captured by the Germans, who later turned them over to the air arm of the independent state of Croatia.
While they were working on the IK-01 in 1933, Ilic and Sivcev had started on a separate project— building a streamlined, low-wing aircraft with retractable landing gear and enough speed and power to intercept the latest generation of bombers. That was also started as a private venture. After Slobodan Zrnic-Zrle, chief of the construction bureau of the airplane factory at Kraljevo, joined the team, the work was shared. Ilic developed aerodynamic calculations; Sivcev concentrated on equipment, tail surfaces and ailerons; and Zrnic focused on cross sections of the fuselage, wings and related structures, as well as engine installation.
The new aircraft was designated the IK-3.The overall idea was to build an airplane that would be very maneuverable rather than fast, which would meet the needs of the Yugoslav fighter pilots. After testing the model in a wind tunnel, the design team chose the 980-hp Hispano Suiza 12Y-29 engine. Documentation was delivered to the air force for approval in 1936, and a contract to finish the prototype was signed in March 1937. After the prototype was completed in the Rogozarski factory in Belgrade, the first flight took place in May 1938. The test pilot, Captain Milan Bjelanovic, declared that the plane, which had a maximum speed of 327 mph, was extremely maneuverable and further said that the control efficiency was very good in all respects.
The result of Ilic, Sivcev and Zrnic’s work looked like a compromise between the British Hawker Hurricane, the German Me-109E and the French Morane Saulnier M.S.406, but it could out turn the Me-109E and was faster than an M.S.406. The new fighter aircraft could climb to 16 ,404 feet in seven minutes. Its armament consisted of one Oerlikon FF 20mm cannon firing through the propeller hub and two 7.9mm Browning/FN machine guns in the upper front fuselage.
On January 19, 1939, the prototype was destroyed in an accident when a test pilot pulled up too violently from a steep dive and the wing broke off; the plane crashed, and the flier was killed instantly. Once again, the adversaries of indigenous Yugoslav-built aircraft objected to the design, and the air force demanded additional static and aerodynamic testing. After a few wasted months, however, the decision to build the first group was confirmed. The initial 12 aircraft were delivered by March 1940. These were followed by another six planes by the end of July. Production IK-3s had some improvements in the front part of the cockpit and the rear end of the fuselage, as well as the addition of maintenance access panels. There were plans to produce 48 IK-3s in 1941 and 1942, and 25 aircraft were under construction when Yugoslavia was invaded.
After the first day of aerial attacks, the German raids continued on April 7 but in smaller bombing formations. Yugoslav fighters changed their tactics, attacking in larger groups, and succeeded in breaking up German formations. Substantial numbers of German aircraft were shot down, but Yugoslav losses were also heavy. The remaining aircraft of the 51st and 32nd Fighter groups (three IK-3s and 11 Me-109Es) flew to the auxiliary airfield at Veliki Radinci near Ruma, where they were burned on the night of April 11 to prevent them from falling into German hands.
At the time of the Axis invasion, one IK-3 airframe was getting a new 1,030-hp Rolls-Royce Merlin III engine, and it was planned to equip all subsequent IK-3s with the 1,100-hp Hispano-Suiza 12Y-51 engine. All experimental IK-3 derivatives, however, were later destroyed to prevent their capture. Also destroyed were all the blueprints and plans for the IK-5 project, a two-engine fighter-reconnaissance aircraft.Testing the IK-5 wind-tunnel model had given excellent results, and the famous designer Igor Sikorsky commented, “ This could be one of the best airplanes ever built.”
The German occupation did not end the story of Yugoslavia’s best prewar fighter.The IK-3’s blueprints survived the war, carefully hidden under the floor of Slobodan Zrnic-Zrle’s house in Belgrade.
After the war, relations between Yugoslavia and the Soviet Union deteriorated because of Marshal Josip Broz Tito’s constant refusal to submit to Soviet “ protection.” In 1948 Yugoslavia was put under an economic blockade by all Socialist countries. On the brink of war, Yugoslavia asked for military aid from the West, but that help— especially in regard to fighter aircraft — was too slow in coming, so the design team of Ilic, Sivcev and Zrnic found itself in business again. They built Model 211 and 212 trainers as well as 45 S-49A fighters developed from the IK-3. In 1951 the S-49A was followed by the more powerful S-49C fighter-bomber, 130 of which were produced. These were withdrawn from service in 1965, thus ending the era of Yugoslav piston-engine fighters.
Originally published in the August 2004 issue of World War II. To subscribe, click here.
