On 21 July 1944, United States Marine and Army forces invaded the island of Guam, the southernmost of the Mariana Islands chain in the Central Pacific, with the intent to take control of the island from the Imperial Japanese Army. Operation Forager II, as it was called by American planners, was a phase of the Pacific Theatre of World War II. The Guam landings had been tentatively set for 18 June but a large Japanese carrier attack and stubborn resistance by the unexpectedly large Japanese garrison on Saipan led to the invasion of Guam being postponed for a month.