The Battle of Heraklion was a battle during World War II on the Greek island of Crete. It began on the morning of 20 May 1941, when Nazi Germany launched an airborne invasion of Crete under the codename Unternehmen Merkur ("Operation Mercury"). British, Australian and Greek forces defended the Heraklion port and airfield. Heraklion was defended by the British 14th Infantry Brigade, augmented by the Australian 2/4th Battalion with attached 2/3rd Light Anti-Aircraft Regiment and the Greek 3rd, 7th and Garrison Battalions.