May 1941 was action-packed. There was the battle for Crete, the Bismarck voyage and destruction, and there was the Tiger Convoy. British resources were stretched to the breaking point. Prior to the German attack on Crete, Wellingtons from No.37, 38, 80, and 148 squadrons flew from Egypt to bomb airfields in Greece every night. Egypt was 300 miles from Crete while Crete was within range of an arc of German air bases.
The German effort would primarily involve the army and air force, as Hitler had decided to leave naval efforts in the Mediterranean Sea to the Italian navy. The air force proposed taking Crete with an airborne attack, and planning proceeded in April and into May. The attack on Crete was named Operation Merkur, and the command was given to General Löhr, commander of Luftflotte 4, with Fliegerkorps VIII and XI. The latter had the airborne troops and their aircraft. The operation included 13,000 troops from the 7th Air Division and 9,000 mountain troops.
Fliegerkorps VIII was equipped with "228 bombers, 205 dive bombers, 114 twin-engined fighters (Me-110), 119 single-engined fighters (probably mostly Me-109), 50 reconnaissance aircraft". The total was 716, of which 514 were serviceable on 17 May. This is based on the account in Vol.II of the Official History.