The Greeks were forced to capitulate, ending resistance on the mainland by the end of the month. Abandoning most of its equipment, the Commonwealth force retreated to the island of Crete. From 20 May, the Germans attacked the island by using paratroops to secure an air bridgehead despite suffering heavy casualties. They then flew in more troops and were able to capture the rest of the island by 1 June. With their victory in the Battle of Crete the Germans had secured their southern flank and turned their attention towards the Soviet Union.