Operation Olympic

Operation Olympic. It was the planned Allied invasion of the southern Japanese island of Kyushu, intended as the first phase of the overarching Operation Downfall. Scheduled for launch on 1 November 1945, codenamed X-Day, the operation aimed to secure airbases and staging areas for the subsequent invasion of Honshu, designated Operation Coronet. The plan was ultimately rendered unnecessary by the conclusion of the Pacific War following the use of atomic bombs and the Soviet–Japanese War.

Background and planning

Planning for the invasion of the Japanese Home Islands began in earnest after the Battle of Okinawa demonstrated the ferocity of expected resistance. The Joint Chiefs of Staff, under the overall command of Douglas MacArthur as Supreme Commander for the Allied Powers, developed the two-phase Operation Downfall. This strategic concept emerged from discussions at the Potsdam Conference and was driven by the belief that only a direct assault would force a surrender, as diplomatic efforts like the Potsdam Declaration were initially rejected. Intelligence from Ultra intercepts and reports from the Office of Strategic Services indicated Japan was preparing for a decisive homeland battle, known as Ketsugō.

Allied invasion force

The assault force, designated the U.S. Sixth Army under General Walter Krueger, was a massive assembly of Allied power. Naval support would be provided by the U.S. Third Fleet under Admiral William F. Halsey Jr. and the U.S. Fifth Fleet under Admiral Raymond A. Spruance, incorporating elements of the British Pacific Fleet. Air supremacy was to be established by the U.S. Strategic Air Forces in the Pacific, commanded by General Carl Spaatz, utilizing bases on Iwo Jima and Okinawa. The initial landing force of fourteen divisions would be supported by Marine units and follow-on troops from the U.S. Eighth Army.

Japanese defenses

Japanese defenses, coordinated by the Second General Army under Field Marshal Hajime Sugiyama, were formidable and deeply entrenched. The Imperial Japanese Army had concentrated the Japanese Sixth Army and other units on Kyushu, fortifying the coastlines and preparing extensive inland positions. The strategy, Ketsugō, called for the use of thousands of kamikaze aircraft, suicide boats, and midget submarines to attack the invasion fleet, while remaining elements of the Combined Fleet would serve as a decoy. Civilian militias were also being mobilized under the aegis of the National Mobilization Law.

Projected course of the operation

The operation planned for simultaneous assaults on three primary beaches in the Miyazaki, Ariake Bay, and Kushikino areas. The goal was to secure the southern third of Kyushu within the first month, including the key ports of Kagoshima and the airfields around Kanoya. Planners anticipated fierce counterattacks from the Imperial Japanese Army Air Service and a high casualty rate from kamikaze strikes, similar to but exceeding the scale of those experienced during the Battle of Leyte Gulf and the Battle of Okinawa. The capture of this territory was considered essential for launching Operation Coronet against the Kantō Plain.

Aftermath and cancellation

The operation was formally canceled after the Surrender of Japan on 2 September 1945, which followed the atomic bombings of Hiroshima and Nagasaki and the Soviet invasion of Manchuria. The high projected casualties for both sides, detailed in studies like the United States Strategic Bombing Survey, became a central point in postwar historical and ethical debates. The successful Occupation of Japan proceeded without the need for the invasion, overseen by Douglas MacArthur's Supreme Commander for the Allied Powers headquarters. The extensive preparations for Operation Downfall left a significant legacy in subsequent Cold War military planning and strategy.

Category:World War II operations and battles of the Pacific theatre Category:Cancelled military operations involving the United States Category:Planned invasions of Japan