Operation Downfall

Operation Downfall was the proposed Allied plan for the invasion of the Japanese home islands near the end of World War II. The planned operation was canceled when Japan surrendered following the atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war and the invasion of Manchuria.[15] The operation had two parts: Operation Olympic and Operation Coronet. Set to begin in November 1945, Operation Olympic was intended to capture the southern third of the southernmost main Japanese island, Kyūshū, with the recently captured island of Okinawa to be used as a staging area. In early 1946 would come Operation Coronet, the planned invasion of the Kantō Plain, near Tokyo, on the main Japanese island of Honshu. Airbases on Kyūshū captured in Operation Olympic would allow land-based air support for Operation Coronet. If Downfall had taken place, it would have been the largest amphibious operation in history.[16]

Operation Downfall
Part of the Pacific Theatre of World War II
Location
Result Canceled after the unconditional surrender of Japan on August 15, 1945
Belligerents
Allies (United Nations):  Empire of Japan
Commanders and leaders
Harry S. Truman
Douglas MacArthur
Chester W. Nimitz
Curtis LeMay
Carl Spaatz
Walter Krueger
Joseph Stilwell
Robert L. Eichelberger
Courtney Hodges
William F. Halsey
Raymond A. Spruance
John H. Towers[3]
Frederick C. Sherman[3]
Richmond K. Turner[4]
Clement Attlee
Bruce Fraser
Bernard Rawlings[5]
Hirohito
Kantarō Suzuki
Naruhiko Higashikuni
Korechika Anami
Mitsumasa Yonai
Yoshijirō Umezu
Soemu Toyoda
Hajime Sugiyama
Shunroku Hata
Seishirō Itagaki
Masakasu Kawabe
Shizuichi Tanaka
Isamu Yokoyama
Keisuke Fujie
Tasuku Okada
Eitaro Uchiyama
Kiichiro Higuchi[5][6]
Units involved

Ground units:

US Army Forces, Pacific

(Up to 58 US and 3-5+ Commonwealth divisions)[7][8]

Naval units:

United States Pacific Fleet

Air units:
USASTAF Pacific

Fifth Air Force
Seventh Air Force
Thirteenth Air Force

Tiger Force

Ground units:

First General Army

Second General Army

Patriotic Citizens' Fighting Corps[6]

(66 divisions, 36 brigades, and 45 regiments, not counting PCFC units.)[10]

Navy units:
Navy General Command

Air units:
Air General Army

  • First Air Army
  • Sixth Air Army

Third Air Fleet
Fifth Air Fleet
Tenth Air Fleet
Sixth Air Fleet

Twelfth Air Fleet[6]
Strength

More than 5,000,000 (projected)[11]
1,000,000 (projected)[12]

More than 6,000,000 total (projected)

4,335,500 military,[13]
31,550,000 civilian conscripts[14]

35,885,500 total

Japan's geography made this invasion plan quite obvious to the Japanese as well; they were able to accurately predict the Allied invasion plans and thus adjust their defensive plan, Operation Ketsugō, accordingly. The Japanese planned an all-out defense of Kyūshū, with little left in reserve for any subsequent defense operations. Casualty predictions varied widely, but were extremely high. Depending on the degree to which Japanese civilians would have resisted the invasion, estimates ran up into the millions for Allied casualties.[17]