In April, Hitler was forced to intervene in the Balkans which led to the campaign of that name; it was also known as the German invasion of Yugoslavia and included the Battle of Greece. The subsequent campaign and the heavy German losses in the Battle of Crete convinced Hitler that air drops behind enemy lines, using paratroopers, were no longer feasible unless surprise was achieved. He acknowledged that the chances of success in an air operation of that kind were low; German airborne forces did not undertake any such operations again. This had important consequences for Malta, as it indicated the island was only at risk from an Axis siege. When, in June, Hitler attacked the Soviet Union under Operation Barbarossa, "Fliegerkorps X" departed for the Eastern Front, and the "Regia Aeronautica" was left to continue its highly effective air campaign against Malta in the coming months. Geisler, commanding the remnants of "Fliegerkorps X", could only count upon mine-laying aircraft from "Kampfgeschwader 4" (KG 4) and Ju 87s in night operations. Supply issues were bad, the small German force left was forced to abandon operations on 22 April 1941. By early May 1941, the "Luftwaffe" had flown 1,465 bomber, 1,144 fighter and 132 reconnaissance missions for just 44 losses. III./"Kampfgeschwader 30" (KG 30) and III./"Lehrgeschwader 1" (KG 1) flew sporadic night attacks during April.