The Battle of Milne Bay (25 August – 7 September 1942), also known as Operation RE by the Japanese, was a battle of the Pacific campaign of World War II. Japanese naval troops, known as Kaigun Rikusentai (Special Naval Landing Forces), attacked the Allied airfields at Milne Bay that had been established on the eastern tip of New Guinea. Due to poor intelligence work, the Japanese miscalculated the size of the predominately Australian garrison and, believing that the airfields were only defended by two or three companies, initially landed a force roughly equivalent in size to one battalion on 25 August. Meanwhile the Allies, forewarned by intelligence from Ultra, had heavily reinforced the garrison.

Despite suffering a significant setback at the outset, when part of the invasion force had its landing craft destroyed by Allied aircraft as they attempted to land on the coast behind the Australian defenders, the Japanese quickly pushed inland and began their advance towards the airfields. Heavy fighting followed as they came up against the Australian Militia troops that formed the first line of defence. These troops were steadily pushed back, but the Australians brought forward veteran Second Australian Imperial Force units that the Japanese had not expected. Allied air superiority helped tip the balance, providing close support to troops in combat and targeting Japanese logistics. Finding themselves outnumbered, lacking supplies and suffering heavy casualties, the Japanese were compelled to withdraw their forces, with fighting coming to an end on 7 September 1942.