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. : 22 The original timetable was optimistic, however. The invasion of Saipan was scheduled for 15 June 1944, with landings on Guam tentatively set for 18 June. B-24 Liberators from the Marianas could also bomb Iwo Jima and the Bonin Islands, such as Chichi Jima.

The seaport at Apra Harbor was suitable for the largest ships and air bases for Boeing B-29 Superfortresses could be built from which to bomb Japan. : 22 Saipan, Tinian, and Guam were chosen as the targets because of their size and suitability as bases for supporting the next stage of operations toward the Philippines, Taiwan, and the Ryukyu Islands. Army Air Forces bombers based in the Marshall Islands to the east, then once air superiority was gained, close bombardment by battleships, cruisers, and destroyers. The United States plan for the invasion of the Marianas, Operation Forager, called for heavy preliminary bombardment, first by carrier aircraft and U.S. But by 1944, Guam had a large Japanese garrison.

During the Japanese occupation of Guam, it was not as heavily fortified as the other Mariana Islands such as Saipan that had been Japanese possessions since the end of World War I. It had been a United States possession since its capture from Spain in 1898 until it was captured by the Japanese on 10 December 1941, following the attack on Pearl Harbor. Guam, at 212 square miles (543 square kilometers), is the largest island of the Marianas, with a length of 32 miles (52 km) and a width ranging from 12 miles (19.31 km) to four miles (6.44 km) at different points of the island. The recapture of Guam and the broader Mariana and Palau Islands campaign resulted in the destruction of much of Japan's naval air power and allowed the United States to establish large airbases from which it could bomb the Japanese home islands with its new strategic bomber, the Boeing B-29 Superfortress. The battle was a critical component of Operation Forager. territory in the Mariana Islands captured by the Japanese from the United States in the First Battle of Guam in 1941 during the Pacific campaign of World War II. The Battle of Guam (21 July–10 August 1944) was the American recapture of the Japanese-held island of Guam, a U.S. Not to be confused with the Battle of Guam (1941).

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