Some of the fiercest fighting in the Pacific Theater of World War II occurred in the campaign to free the Palau and Mariana islands between June 1944 and November 1944. The overall offensive was led by Admiral Chester Nimitz who commanded U.S. Navy, U.S. Army, and U.S. Marine Corps forces against the Imperial Forces of Japan in the Pacific.
This was directly after the Marshall and Gilbert Island campaign, and the U.S. Forces in the region were gaining momentum. The Mariana campaign was intended to neutralize the bases in the region that Japan had already established, and give the Allied efforts to reclaim the Philippines some energy as well as providing additional United States and Allied bases from which to mount a bombing campaign against Japanese forces. United States Army forces, with support from the U.S. Marines and U.S. Navy began to stage a series of landings on Saipan during the month of June 1944.
The Japanese Navy was less than thrilled with the action and they struck back trying to attack and destroy the Naval battle fleet of the United States that were supporting the U.S. Army landings. In a mighty battle between aircraft carriers and their aircraft, the Battle of the Philippine Sea occurred during the two-day period of June 19 and 20th, 1944, where the Japanese Imperial Fleet was defeated with sharp losses to their land based and carrier based aircraft.
After the successes at Marshall and Gilbert Islands, and the success of the Philippine Sea encounter, the U.S. Army stepped up efforts to execute more landings on Tinian and Guam in July 1944. Saipan was finally secured also in July 1944 and then the U.S. Army forces were able to secure Tinian and Guam also later in August 1944. Important strategic airfields were constructed by Army and Army Corps of engineer personnel working round the clock to make landing places for B-29 bombers to conduct strategic bombing missions from. These missions were made possible because of the hard work and sacrifice from the various Army units that counted the cost and made the Tinian and Saipan Islands secure.
U.S. Army Soldiers accompanied by U.S. Marine Amphibious units landed later on Angaur and Peleiiu in the Palau region. There was intense combat and fairly heavy losses by Army units on Peleliu, but U.S. Army Force finally secured it in November 1944.