In May 1941, Nazi Germany began an airborne invasion of Crete against Greek and other Allied forces. Initially, the Germans suffered heavy casualties and the Allied troops were confident that they would defeat the invasion. However, a series of communication failures, Allied tactical hesitation and German offensive operations enabled the Germans to overwhelm the Allied forces. The Battle of Crete was the first occasion where German paratroops were used en masse and was the first mainly airborne invasion in military history.