Bombing and bombardment of Saipan began on June 13 1944. Fifteen battleships were involved, and 165,000 shells were fired. The landings began at 07:00 on June 15 1944. More than 300 LVTs landed 8,000 marines on the west coast of Saipan by about 09:00. Careful Japanese artillery preparation — placing flags in the bay to indicate the range — allowed them to destroy about 20 amphibious tanks, but by nightfall the marines had a beachhead about 10 km wide and 1 km deep. The Japanese counter-attacked at night but were repulsed with heavy losses. On 16 June units of the U.S. Army’s 27th Infantry Division landed and advanced on the Aslito airfield. Again the Japanese counter-attacked at night. On 18 June Saito abandoned the airfield.
The invasion surprised the Japanese, who had been expecting an attack further south. Admiral Toyoda Soemu, commander-in-chief of the Japanese Navy, saw an opportunity to use the A-Go force to attack the U.S. Navy forces around Saipan. On 15 June he gave the order to attack. But the resulting battle of the Philippine Sea was a disaster for the Imperial Japanese Navy, which lost three aircraft carriers and hundreds of planes. The garrisons of the Marianas would have no hope of resupply or reinforcement.
Without resupply, the battle on Saipan was hopeless for the defenders. But the Japanese determined to fight to the last man. Saito organized his troops into a line anchored on Mount Tapotchau in the defensible mountainous terrain of central Saipan. The nicknames given by the Americans to the features of the battle — “Hell’s Pocket”, “Purple Heart Ridge” and “Death Valley” — indicate the severity of the fighting. The Japanese used the many caves in the volcanic landscape to delay the attackers, by hiding during the day and making sorties at night. The Americans gradually developed tactics for clearing the caves by using flamethrower teams supported by artillery and machine guns.
Navajo codetalkers played a key role in directing naval gunfire onto Japanese positions. By 7 July the Japanese had nowhere to retreat to. Saito ordered his remaining able-bodied troops — about 3,000 men — forward in a suicide charge, then killed himself. Many hundreds of Japanese civilians committed suicide in the last days of the battle, some jumping from “Suicide Cliff”. Efforts by U.S. troops to persuade them to surrender instead were mostly futile.
After the battle, Saipan became an important base for further operations in the Marianas, and then for the invasion of the Philippines in October 1944. Bombers based at Saipan attacked the Philippines, the Ryukyu Islands and Japan. Japanese Army Captain Sakeo Oba held out in the mountains with forty-six men until he surrendered on December 1 1945.