Devastation in Tokyo following US Army Air Force firebombing in March 1945 Operation Downfall Allied plan for the invasion of the Japanese home islands near the end of World War II .
The operation had two parts, Operation Olympic , intended to capture the southern third of the southernmost main Japanese island, Kyūshū , and Operation Coronet , the planned invasion of the Kantō Plain , near Tokyo , on the main Japanese island of Honshu . Olympic was scheduled for November 1945, to be followed by Coronet in early 1946.
If Downfall had taken place, it would have been the largest amphibious operation in history, surpassing D-Day .[1] Japan surrendered following the atomic bombings of Hiroshima and Nagasaki , the Soviet declaration of war , and the invasion of Manchuria .[2]
Order of Battle for Olympic
Allied
Supreme Commander, Allied Forces Pacific General Douglas MacArthur
Ground forces
Should these four corps prove insufficient to accomplish the tasks assigned, elements earmarked for Coronet would be used to reinforce Sixth Army at the rate of three divisions per month beginning about 30 days after the initial landings.
Sixth Army General Walter Krueger [3] Peripheral landings
40th Infantry "Sunburst" Division (Landing on Yakushima and Koshikijima Islands )158th Infantry Regiment (Landing on Tanegashima )
I Corps Miyazaki )[3] Major General Innis P. Swift 25th Infantry "Tropic Lightning" Division 33rd Infantry "Illinois" Division 41st Infantry "Sunsetters" Division
V Amphibious Corps Kushikino )[3] Major General Harry Schmidt , USMC3rd Marine Division (Bougainville , Guam , Iwo Jima )4th Marine Division (Kwajalein , Saipan /Tinian , Iwo Jima )5th Marine Division (Iwo Jima )
XI Corps Ariake )[3] Major General Charles P. Hall 1st Cavalry Division Americal Division 43rd Infantry "Winged Victory" Division
IX Corps [3] Major General Charles W. Ryder 81st Infantry "Wildcat" Division 98th Infantry "Iroquois" Division
Follow-up units:
11th Airborne Division 77th Infantry Division
Naval forces
Third Fleet Admiral William F. Halsey 20 fleet and light aircraft carriers
9 battleships
26 cruisers
75 destroyers
incl. British Pacific Fleet
6 fleet and light carriers
Fifth Fleet Admiral Raymond A. Spruance 36 escort carriers
11 battleships
26 cruisers
387 destroyers and destroyer escorts
394 AKA , AP, APA, APD, APH
977 LSD , LSM , LST , and LSV
Seventh Fleet Admiral Thomas C. Kinkaid
Air forces
George C. Kenney as a full general
Carl Spaatz as a full general
Far East Air Forces General George C. Kenney Fifth Air Force Seventh Air Force Thirteenth Air Force
United States Strategic Air Forces in the Pacific General Carl A. Spaatz
Major General Curtis E. LeMay [a] Twentieth Air Force (Lt. Gen. Nathan Twining ) (77,000 men)
1,000 B-29 Superfortresses Eighth Air Force (Lt. Gen. Jimmy Doolittle )
Commonwealth forcesTiger Force (detached from RAF Bomber Command ):
480–580 Avro Lancaster bombers (about half to be used as tankers for in-flight refuelling ) Australian First Tactical Air Force
20 fighter/attack squadrons from the Royal Australian Air Force
Japan
Ground forces
Field Marshal Shunroku Hata Second General Army Field Marshal Shunroku Hata [b] Sixteenth Area Army Lieut. General Yokoyama Isamu (600,000 men)
Northern Kyūshū — 56th Army Lieut. General Ichiro Shichida (365,000)[4] 145th Division 312th Division 351st Division 124th Independent Mixed Brigade
57th Division (20,000 men)4th Tank Brigade
Southeastern Kyūshū — 57th Army Lieut. General Nishihara Kanji (150,000 men)
Tanegashima—109th Independent Mixed Brigade (5,900 men)
Miyazaki—154th Division , 156th Division, 212th Division [4]
Ariake—86th Division , 98th Independent Mixed Brigade, 1 regiment, 3 infantry battalions (29,000 men)
25th Division , 5th Tank Brigade, 6th Tank Brigade[4]
Southwestern Kyūshū — 40th Army Lieut. General Nakazawa Mitsuo (85,000 men)
303rd Division (12,000 men) (Sendai )206th Division (Fukiage )146th Division , 125th Independent Mixed Brigade (S. Satsuma Peninsula)77th Division [4]
216th Division [4]
Air forces
Air General Army General Masakazu Kawabe Sixth Air Army — Kyūshū
5,000 aircraft assigned as kamikazes , 5,000 aircraft available for kamikaze service, 7,000 aircraft in need of repair
100 Koryu -class midget submarines, 250 Kairyu Kaiten manned torpedoes, 800 Shinyo suicide boats
Order of Battle for Coronet
Allied
Ground forces
Gen. Courtney H. Hodges as a major general
Lt. Gen. Robert L. Eichelberger
First Army General Courtney H. Hodges [3] [c] III Amphibious Corps [3] 1st Marine Division (Guadalcanal , Peleliu , Okinawa )2nd Marine Division (Tarawa , Saipan , Okinawa )6th Marine Division (Okinawa )XXIV Corps [3] 7th Infantry "Bayonet" Division 27th Infantry "New York" Division 96th Infantry "Columbia" Division Eighth Army Lieut. General Robert L. Eichelberger
X Corps [3] 24th Infantry "Taro" Division 31st Infantry "Dixie" Division 37th Infantry "Buckeye" Division XIV Corps [3] 6th Infantry "Red Star" Division 32nd Infantry "Red Arrow" Division 38th Infantry "Cyclone" Division XIII Corps [3] 13th Armored Division 20th Armored Division United States Army Forces Pacific reserve[3] 97th Infantry "Trident" Division Thirty days after the initial assault, each army would be reinforced by a corps of 3 divisions. Five days later an airborne division and a United States Army Forces Pacific Reserve Corps of 3 divisions would be made available. Strategic reserve for the entire operation would consist of a corps of 3 divisions located in the Philippines and divisions from the United States to permit reinforcement at the rate of 4 per month.[3]
Unsourced listing of the aforementioned reinforcements
For First Army
Unnamed follow-on corps
5th Infantry Division 44th Infantry Division 86th Infantry Division For Eighth Army
Unnamed follow-on corps
4th Infantry Division 8th Infantry Division 87th Infantry Division United States Army Forces Pacific reserve
11th Airborne Division Unnamed follow-on corps
2nd Infantry Division 28th Infantry Division 35th Infantry Division
Strategic reserve
91st Infantry Division 95th Infantry Division 104th Infantry Division British Commonwealth Ground Forces
Commonwealth Corps (Lt. Gen. Charles Keightley )
3rd Infantry Division (United Kingdom) 6th Infantry Division (Canada) 10th Infantry Division (Australia)
Japan
Field Marshal Hajime Sugiyama
All Japanese formations on Honshu were badly understrength and lacking in equipment. The American First Army's landings would likely have been opposed by the Japanese 52nd Army and the Eighth Army's landings by the Japanese 53rd Army.
First General Army Field Marshal Hajime Sugiyama [d] Twelfth Area Army General Shizuichi Tanaka [e] 36th Army Saitama
81st Division 93rd Division 201st Division 202nd Division 206th Division 214th Division 1st Tank Division 4th Tank Division 51st Army Tsuchiura , Ibaraki
44th Division – Ogawa 151st Division – Mito 221st Division – Kashima 115th Independent Mixed Brigade – Shibasaki
116th Independent Mixed Brigade – Hokota
7th Independent Armored Brigade – Ogawa 52nd Army Sakura , Chiba
3rd Imperial Guards Division – Naruto
147th Division – Mobara 152nd Division – Choshi 234th Division – Sōsa 3rd Independent Armored Brigade
8th Artillery Headquarters 53rd Army Isehara , Kanagawa
84th Division – Odarawa140th Division – Kamakura 316th Division – Isehara117th Independent Mixed Brigade – Numazu
2nd Independent Armored Brigade – Tsudanuma
11th Artillery Headquarters – Hiratsuka Tokyo Bay Garrison – Choshi , Chiba
321st Division – Tokyoa 
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