Guam

Largest and most populated of the Mariana Islands, acquired by the United States as a prize of war from Spain in 1899. Guam functioned as an advance base of increasing importance for the U.S. Navy as Japan figured more prominently in war planning in the years and months immediately prior to World War II. Guam remained unfortified and vulnerable under the 1922 Washington Treaty. Easily taken by Japan in 1941, Guam formed part of the island barrier chain that defended the Japanese Empire from the Allied counteroffensives of 1944.

As would happen so many times in the Pacific during World War II, no sooner had U.S. forces oriented to a new set of operational challenges than the situation changed. From attacking isolated Japanese garrisons on coral atolls, the III and V Amphibious Corps of the Marine Corps turned, in mid-1944, to confronting large units of the Japanese army, defending large Pacific islands that presented all possible variations of terrain.

The Mariana Islands formed the inner island defense barrier of Japanese strategy for the Pacific war, and a decisive battle fought on land, at sea, and in the air settled the fate of the Japanese Empire. Although U.S. Navy submarine and air interdiction prevented Japanese reinforcements and key fortification materials from reaching the islands in the early part of 1944, the garrisons already in place boasted reinforcing artillery, tanks, and other arms, including naval infantry.

The U.S. invasion force, the largest yet assembled in the Pacific, targeted three large islands for Operation Forager: Saipan and nearby Tinian in the northern archipelago and Guam in the south. The III Amphibious Corps landed on Guam with the Third Marine Division and the First Provisional Marine Brigade, with the Army's 77th Infantry Division, held initially at Hawaii, in reserve.

The parallel assault on Guam began July 21, 1944, a few days before the V Amphibious Corps hit Tinian. The landing force benefited from the delays imposed while the Fifth Fleet fought off the Japanese Navy in the Battle of the Philippine Sea. In addition, better reconnaissance information and aerial photography had reached the unit commanders. A 13-day naval and air bombardment, the longest of the Pacific war, softened Guam's defenses before Major General Roy Geiger's III Amphibious Corps began its storm landing. The clearing of Guam took 20 days, and the 77th Division reinforced the Marine Corps units after the main landings occurred.

After the recapture of Guam from the Japanese, the United States rebuilt and expanded its military facilities [Page 307]on the island as the forward command and logistical center for the western Pacific. It also served as the base for the last amphibious assaults against Japan in 1945, including the planned invasions of the home islands.

Since the end of World War II, Guam has remained the major western Pacific outpost of the U.S. Navy and, with the abandonment of bases in the Philippines, the U.S. Air Force as well. By the end of the 20th century, the United States had experienced significant losses in access to or use of overseas bases in other countries, so the relative importance of Guam redoubled as the sole U.S. sovereign territory in the western Pacific.

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