U.S. Marines Launch Invasion of Saipan

Context

By early 1944, American strategy in the Pacific had shifted toward a central thrust through Micronesia after successes in the Gilbert and Marshall Islands. Planners under Admiral Chester Nimitz sought bases in the Mariana Islands to support long-range B-29 Superfortress operations against the Japanese home islands, a goal endorsed at Allied conferences despite competing priorities from General Douglas MacArthur’s Southwest Pacific drive. The islands formed part of Japan’s Absolute National Defense Zone, intended to be held at all costs to protect supply lines and keep American forces beyond bomber range.

What Happened

Operation Forager began with pre-invasion carrier raids that neutralized much of the Japanese air presence on Saipan. On June 15, after two days of naval bombardment, the 2nd and 4th Marine Divisions landed on the southwest coast near Charan Kanoa, supported by the 27th Infantry Division held in reserve. Japanese defenders under Lieutenant General Yoshitsugu Saitō, numbering roughly 31,000 army and navy personnel, met the assault with heavy artillery and machine-gun fire from prepared positions and the heights overlooking the beaches, causing thousands of American casualties on the first day. The Marines nevertheless established beachheads and began advancing inland against determined resistance.

Aftermath

The landings immediately drew out the Japanese fleet, leading to the Battle of the Philippine Sea on June 19–20, in which U.S. carrier aircraft destroyed much of Japan’s remaining naval airpower. Fighting on Saipan continued for nearly a month as American forces cleared rugged terrain around Mount Tapotchau and confined the defenders to the northern end of the island. A large-scale Japanese counterattack on July 6–7 was repulsed with heavy losses, and organized resistance ended on July 9.

Legacy

Saipan’s capture provided forward bases that enabled sustained B-29 bombing of Japan beginning in November 1944, altering the strategic balance and contributing to Prime Minister Hideki Tōjō’s resignation. The campaign refined amphibious tactics refined since Guadalcanal and underscored the high cost of island fighting, influencing later planning for operations such as the projected invasion of Japan. It also forced Japanese leaders to acknowledge publicly that the war was not proceeding favorably.