Operation Downfall: How Long Would Japan Have Resisted An Allied Invasion?

Operation Downfall, the planned Allied invasion of Japan during World War II, was scheduled to begin in November 1945. This grand operation was expected to involve extensive ground combat, yet the timeline for Japan's eventual surrender was uncertain and highly dependent on a myriad of factors.

Casualty Estimates

Alleged planners anticipated enormous losses on both sides. The U.S. estimated that its forces could suffer hundreds of thousands of casualties, while Japanese losses were expected to be even more significant due to their anticipated fierce resistance.

Duration of Combat

The scale of the operation, including the invasion of Kyushu (Operation Olympic) and the subsequent invasion of Honshu (Operation Coronet), could have lasted for months or possibly longer. The duration would have depended significantly on the level of Japanese resistance and the effectiveness of Allied forces.

Japanese Resolve

Japan's leadership was committed to fighting to the end, and it was uncertain how long this resolve would hold in the face of a full-scale invasion. The Japanese military had at least 21 divisions ready for land defence, indicating a strong will to resist.

Impact of Other Factors

The strategic use of atomic bombs on Hiroshima and Nagasaki in August 1945 played a significant role in the decision for Japan to surrender. Without these bombings, it is likely that Operation Downfall would have prolonged the war, potentially for another 12 months, from November 1945 onwards.

Historical Context

Post-war documents reveal that the Japanese Command had planned a reinforced defence of Kyushu, intending to inflict such high American casualties that the U.S. would request an armistice. This strategy would have mirrored their tactics on Iwo Jima and Okinawa, but with a significant increase in Kamikaze air attacks. Even if the atomic bombs were not available, the destruction and death anticipated would have unmatched anything in the history of warfare.

Considering these factors, it is clear that Operation Downfall would have significantly impacted the duration of the war. Japan's ability to sustain a prolonged resistance was a major concern for Allied planners, and the outcome would have been marked by immense human cost on both sides. The operation's timeline and outcome were deeply intertwined with the available strategic options and the ultimate decision to use the atomic bombs.