 That preparations were being made was revealed on 7 February through the decryption of "Luftwaffe" Enigma messages but by 23 March the scare died down and more bombing was expected.By 31 March the progress of the Axis bombing campaign led to a prediction that the attempt would be made in April but this was soon discounted because although the bombing offensive increased from in February, to in March, in April, Enigma decodes showed that there were still aircraft in Sicily, not the originally intended, because aircraft were detained in Russia by the Soviet winter offensive and on 26 April, Enigma revealed that "Fliegerkorps" II was being withdrawn.By 2 May, a "Luftwaffe" bomber group and a fighter group had been withdrawn with more to follow, which explained the lull.