 Complete the following phrase:  It became difficult to continue activity from the 51st Fighter Group airfield at Zemun due to air attacks, so on 8 April the remaining IK-3s and Bf 109Es flew to an auxiliary airfield at Veliki Radinci, north-west of Belgrade, where the surviving aircraft of the 6th Fighter Regiment were concentrated. Poor weather made operations impossible until 11 April, when Semiz shot down a Bf 110 that had strafed the airfield. Later that day, Gogić and another IK-3 pilot claimed one Ju 87 each during a patrol. That night, German troops approached within of the airfield at Veliki Radinci and the following day all remaining aircraft of the 6th Fighter Regiment, including the remaining IK-3s, were burned by their crews. According to aviation writers Dragan Savić and Boris Ciglić, one serviceable IK-3 was captured by the Germans in April 1941 and it was joined by another by the end of June. Both aircraft were located at Zemun, along with 23 other former VVKJ aircraft in working condition that were destined for service with the air force of the Axis puppet state, the Independent State of Croatia. The Germans had used a fence to separate the serviceable aircraft from other aircraft that had been earmarked for scrapping. In late June, while the German guards were distracted listening to news of 