World War II in the Pacific
Operation Downfall : Olympic and Coronet
The Invasion of Japan
OPERATION DOWNFALL, to be complete within one year of the
end of the war in Europe, had two major components.
Olympic . November 1, 1945. Invasion of Southern Kyushu to provide
a large base for naval and air forces within range of Tokyo.
Coronet . March 1, 1946. Invasion of Central Honshu and Tokyo.
Background. Japan had captured most of the Pacific in their first
six months of conquest ; were stopped at Coral Sea ; bloodied at Midway ; reversed at Guadalcanal.
The Japanese fought fiercely to maintain her empire as American
arms destroyed her naval, air, and merchant fleets. There were two
drives, one by MacArthur, Army, from New Guinea to the north to return to
the Philippines. A second by Nimitz, Navy, from Hawaii west across the
central Pacific to obtain air bases in the Marianas within B-29 range
By the beginning of 1945, Japan had been defeated
but would not surrender. The steps of the end game entailed:
24Nov44. Start B-29 raids on Japan from Marianas.
Feb 19-Mar 16. Iwo Jima to provide a fighter escort base within range
of Japan and an emergency landing field for damaged B-29's.
Mar 6-end. Incineration of industrial capacity.
Apr 1-Jun 21. Okinawa to provide a base for attack planes to cover the
the capture of the southmost main island, Kyushu.
May 8 . Germany surrenders. The Pacific, 1-year clock starts.
May 13. Isolation of Kyushu from reinforcement starts with aerial mining.
July 13. Isolation of Japan from their bases in China and Korea by mining.
July 19-28. Destruction of the remaining fleet in home waters.
Aug 06/09. Unexpected use of secret weapon, an atomic bomb.
Aug 14 . Surrender of Japan.
Olympic entailed landing three corps on southern
Kyushu, the most southern of the four Japanese home islands.
The center portion of Kyushu is almost impassible mountains
which would be difficult to transit and was to be used to isolate
southern Kyushu from counterattack by Japanese troops from northern
Kyushu (Nagasaki). The landings were to be by troops already in
the Pacific covered by 34 carriers and by land based aircraft from
Okinawa. B-29's would interdict reinforcements. Southern Kyushu
had a large bay, harbors, and many airfields. The intent
was to base naval support craft and to establish 40 air groups,
many redeployed from Europe. From southern Kyushu, fighter air cover
could open the Inland Sea to the US Navy and interdict transportation
as far as north as Osaka ;
fighter bombers could close shipping from Korea and China ;
medium bombers and could destroy transportation, material, and
installations around Tokyo and support the invasion troops ;
large bombers (B-17 and B-24) could range over all of Japan.
Meanwhile, B-29's from the Marianas could continue to wipe out
There were two naval groups.
The Strike Force, 3rd Fleet, had 21 carriers and 10 fast battleships
to range up and down the length of Japan to suppress Japanese forces with
priority to destroy aircraft and transportation.
The Assault Force, 5th Fleet, had 26 carriers, plus 8 detached from Strike force for the invasion
period, 13 slow battleships, 20 cruisers, 139 DD, 167 DE, and support ships
for a total of 800 warships. Troops and their equipment were to come from
the Philippines and Marianas in 1,500 transports. All combat troops were from
the Pacific theater ; none redeployed from Europe. The plan called
for a diversionary display by the floating reserve on Shikoku,
the smallest of Japan's four islands, before their landing on Kyushu.
Support troops including engineers to build airfields were to
land starting on Y-Day + 2 ; some of these were to come from Europe.
The Japanese Defenses At the time of the start to planning of Olympic, there were 1-1/2
divisions based on southern Kyushu; these with various service bases there
amounted to about 45,000 men. Planners expected an additional
three divisions to be moved into the area by the time of the landings.
The Japanese were able to predict the landing using the same logic
as US planners and moved 9 more divisions into the area for 216,000 men
by the time of the surrender in august. More men, material and defenses
would have been assembled by the November date for the invasion.
Each side of the central bay had an army, each was divided into
two functions - a static defense force on the beaches to fight
to the death while allowing reinforcements to arrive, and the
mobile reserve to push the American back into the sea.
The three logical landing beaches were defended from the shore to
the nearby mountains with new troops. The reserves located
in the mountains were experienced troops from Manchuria with light
Supporting the troops were the remnants of the navy and air force,
lightly armed volunteers, and an array of "special" weapons.
The air forces contained 5,600 conventional combat
planes and a similar number of older planes and trainers suitable
as Kamikazes. The combat planes were withdrawn from Kyushu
and the Kamikazes moved in. Japan was so short of aircraft and fuel
that B-29's and carrier task forces were not routinely attacked so
as to conserve combat aircraft for the final battle.
Equal numbers were assigned to Kyushu and
Tokyo areas. As the date for the first battle approached, more were
moved to Kyushu with the Tokyo forces to be replaced with promised
Kamikaze tactics were initiated in the Philippines
and became a doctrine that inflicted terrible damage to US warships off
Okinawa. The invasion of Kyushu would see the distance
reduced, flying over familiar land instead of over-water navigation,
and with targeting changed from warships to troopships ; the plan
was to inflict intolerable damage to the invasion force before it
hit the beach.
The following "special weapons" were established on southern Kyushu.
Kamikazes -- 2,100 army planes and 2,700 navy planes.
Baku - suicide missile carried by a bomber.
Mini-subs, each with 2 torpedoes, 500 were building.
Fleet submarines -- rearm the 57 remaining that had been dedicated to resupply of outposts.
Kaiten - suicide torpedoes with a 20 mile range.
Shinyo - suicide motorboats. The army had 1-man, 17 foot motorboats.
The navy had 2-man, 22 foot boats.
The largest surviving warships were destroyers that were prepared for
suicidal attack on the invasion convoys.
On the land, human mines in which soldiers had explosives strapped
to their bodies and were to crawl under a tank. Other explosives were packed
with a suction cup to be attached to the side of a tank. And shaped charges
on a long pole were to be detonated on the side of a tank.
Japanese paratroopers were to attack Okinawa to disrupt flight operations during
the invasion period.
Alternatives to Olympic. Rather than invade Japan, the country could have been
blockaded with a ring around the Yellow Sea from Shanghai to Korea.
This was not assured to cause the surrender of Japan. The direction
of the war would have been towards reinforcing China and supplying the
Soviet Union for their movement of troops into Manchuria, Korea,
and mainland China.
A plan resurrected after the enemy buildup on
Kyushu exceeded all expectations, was the occupation of the less well
defended northern island of Hokkaido and northern part of Honshu.
This would have been of equal distance from Tokyo, but further from
American army, naval, and air force centers.
Shipping was already a problem with large numbers unreleased from
the Atlantic needed to supply Europe and return troops to the US ; to redeploy
air and service forces from Europe to the Pacific, to supply the
Pacific buildup and to move several corps to the invasion sites.
Every tanker in the US fleet was required to provide the millions of
gallons of fuel required by the ships involved in the Kyushu
operation. More fuel and shipping would be required to move 1,100 miles further
away to the north. That plan was dropped.
Casualties. There are two sets of potential casualty figures;
a low number used to gain approval to proceed with the
operation ; and a high number used to plan reserve forces, medical
needs and, as it turned out, to claim as lives saved by use of the
atom bomb. These figures changed over time, starting low and
going higher as the enemy build-up on Kyushu was discovered.
The low casualty figures were based on the
landings at Okinawa, Lingayen Gulf, and Normandy. Okinawa and Lingayen
Gulf were undefended on the beaches, the fighting took place in the
mountains where each Japanese caused one US wounded of which 20% resulted in US deaths.
Normandy had the same three-beach landing pattern, but
two beaches were relatively easy, only the landing at "bloody" Omaha
was vigorously defended. All three Kyushu beaches were defended in
depth. A shoreline defense such as Omaha beach and a mountain cave
defense as on Okinawa ; all to the death.
It would have been more realistic to triple the rate of Omaha beach
rather than take the average of the three Normandy beaches as the
planners did. There was also a difference in scale.
Normandy landed 5 divisions plus 3 airborne divisions.
Olympic was to land 14 divisions. Coronet was to have 23 divisions.
The defended beach at Tarawa was
a shock to Marine landing with unexpected losses. The US invasion
tactic was then changed from surprise to heavy bombardment. The
Japanese had to change their defensive positions in the later Pacific
actions from defense of the beach to the mountains. Kyushu was to have both
forms of defense: well prepared installations near the beaches and
well prepared caves in the mountains, with mobile tank forces.
The US planners expected that radar would detect
Kamikazes coming through the mountains, carrier fighters would
be vectored to intercept them, and proximity-fused ship's
anti-aircraft fire would take out any that got through. However,
250 highly maneuverable warships were hit a few months earlier
at Okinawa with these same defenses, in open water ; the prospects
of loaded troop ships taking casualties was high and each hit
could take half-a-thousand lives.
Whereas two Messerschmitts were able to attack troops on the Normandy
beaches, 5,000 Kamikaze were aimed at the approaching troop ships
while still at sea.
It would be reasonable to increase the hit
rate of Kamikazes from nearby bases, yet the planners reduced it.
Japanese planners expected almost 500 ships would be
sunk during the landing. US planners expected 15-20% losses, they
had no experience with mass air attacks on merchant ships at sea.
Good weather was required for close air support
on the cloudy islands of Japan. A typhoon had once saved Kyushu
from invasion by Mongols in 1281. A storm that forced the carriers
to withdraw or even to cause the 2,000 planes to remain on deck,
would take away an important part of the invasion support. A storm
would also hamper getting supplies over the beaches to the armies.
The original plan was for 9 divisions to attack 3 divisions of defenders.
As enemy reinforcements were observed, the size of the invasion
force was increased. The final plan had 18 U.S. divisions attacking 11
IJA divisions in defensive positions. Most sources give the advantage to
defenders by 3:1, that is, attackers must outnumber defenders by three
to be sure of victory.
Casualty figures were a guess that changed with
time. There are sufficient numbers available to support any post-war
position that any author chooses to take. Low numbers are quoted
as reasons to do the invasion, 125,000 for Olympic and to end the war.
High numbers, one million US casualties for Downfall, are quoted to justify
the A-bomb and end the war. Typically, 25% of casualties are deaths.
On average, 5 Japanese soldiers died for each American death.
Japanese casualties were not subjected
to planning. If all troops resisted to the death, then the
typical survival rate would have only included injured and unconscious
soldiers. 216,627 troops were surrendered on Kyushu alone -- more than
were expected -- and this was two months before the planned invasion
so the number of defenders would have increased.
Civilian casualties are a real unknown. 97,000 were killed in the
bombing of Tokyo on March 9 ; the numbers
from land warfare would also be high. Consider ratios of any
proportion you desire. Civilian losses in some European cities
were considerable ; certainly Japanese casualties would be
in the multiple millions.
CORONET -- Spring 1945
Coronet was the attack across the Kanto plain to capture Tokyo.
The broad plan was still going through refinement.
Naval bombardment by guns and air would begin at Y-15.
There would be two simultaneous assaults on Y day.
First Army was to land on the southern half of Kujukuri Beach with 4 divisions
to secure a beachhead. On Y+5, with two more divisions landed, they would move
across the peninsula to clear the east side of Tokyo Bay and move north to take
the port city of Choshi. Service troops would built land-based air bases under
the cover of carrier aircraft. Thirty air groups were expected to be in place by Y+30.
Almost simultaneously, Eighth Army would land at Sagami Bay with four divisions
to establish a beachhead, secure the Miura Peninsula and Yokosuka naval base.
At Y+10, two armored divisions would land and move straight north, beind the industrial cities
on Toyko Bay, to establish
a blocking position north of Tokyo. Other elements were tasked to take the port
cities of Yokohama and Kawasaki to provide supply points for the troops.
First Army was to attack across the Kanto plain to Tokyo
about Y+30 with Eighth Army tanks ready to provide assistance. Tokyo had already
been extensively destroyed by bombing.
Coronet was a larger operation than Olympic, but the landing on Kyushu,
the southern island, was expected
to be the more expensive because all of the homeland defensives would have been expended
there and the promised replacements to ward off Coronet would have been made industrially
impossible. Several thousand Air Force fighters and medium bombers would be flying from a hundred airfields on Kyushu. A 100 carriers could have been available including new construction and those coming from the Atlantic.
The Joint Chiefs expected the Japanese to surrender after exhausting themselves
in Operation Olympic. Thus Coronet would not be required.
However, if necessary, follow up operations after Tokyo would have
been initiated in the south, central, and north of Japan with US troops from Europe
who had taken leave in the US -- only Air Force, air field construction, and service units
had gone from Europe directly to the Pacific. And troops from Allied countries would be available.
South. The northern, more industrialized half of Kyushu would have been taken.
Central. The next largest industrial cities would have been taken with landings
to take the peninsulas of Ise Bay, take Nagoya and then march overland to Osaka,
Kyoto and Kobe.
North. A landing at Sapporo on Hokkaido followed by taking the anchorage at Mautsu.
Hindsight . Capture of the Marianas as B-29 bases
turned out to be the key to the end-game. The campaign in the
Philippines and Peleliu were not necessary except to force the
final battle with the Japanese fleet and as a place to absorb Japanese
army troops and air forces for destruction. Also, an alternative
considered at the time, the invasion of Formosa to open access to
China and as an alternate base for B-29's would have been equally
unnecessary. These resources could have been applied sooner to
capture and build air bases at Saipan, Iwo Jima and Okinawa, which
were instrumental in the rapid end of the war. But the secret
weapon was a secret and it might not have worked or been ready in time.
Olympic - Southern Kyushu Troops . All were US from Pacific area
Autumn of 1945 6th Army.
Sep 1 . Honshu, Kyushu, Strategic Air Force (B-29 Okinawa) ; continue strategic targets.
Sep 1 . Shimonoseki Straight / ports, Strategic Air Force ; continue isolation mining.
Sep 18. Hong Kong , British strikes.
Sep 28. Canton , British strikes.
Oct 1 . Ningpo , Chusan, China , Strategic Air Force ; isolation bombing.
Oct 18. Honshu, Inland Sea , 3rd Fleet : TF-38 (US) , TF-37 (UK) ; strategic support
Oct 21. Kyushu , Strategic Air Force ; N-S isolation and anti-buildup
Oct 24. Kyushu , 5th Fleet ; preliminary bombardment, mine clearing, interdict highways.
Oct 27. Outer Islands , 40th Inf Div
Oct 28. Tanega Shima , 158th Reg Combat Team
Oct 30. Shikoku , feint by 9th Corp : 77th , 81st , 98th Infantry Divisions
Nov 1 . West , 5th Amphibious Corp : 2nd , 3rd , 5th Marine Divisions
Nov 1 . South , 11th Corp : 1st Cav , 43rd Inf , Americal Divisions.
Nov 1 . East , 1st Corp : 25th , 33rd , 41st Infantry divisions
Nov 22. Where needed : 11th Airborn Division.
Nov 23. As needed or SW : 9th Corp : 77th , 81st , 98th Infantry Divisions
Dec - . Build air fields : support troops and air crews from European theator.
Jan - . Attack all military and industrial areas of Japan by air and sea.
Further Information. See the short version of this page. "The Invasion of Japan:" by John Ray Skates, U of So Carolina Press, 1994.
Well researched but seems to draw the conclusion that invasion was cheaper than the bomb. [to whom?]
"Code-Name Downfall: The Secret Plan to Invade Japan and why Truman
Dropped the Bomb" by Thomas B. Allen and Norman Polmar, Simon & Schuster, 1995
There have been many magazine articles over the years.
There are many differences in various reports because
Operation Downfall was a plan that evolved over various times.
Check the web, there are lots of sites shown by a search.
Planning Alternatives for Coronet -- Spring of 1946 Coronet was the attack across the Kanto plain to capture Tokyo.
The broad plan was still going through refinement and only outline drafts had been completed by August 1..
The initial plan called for three landings using 25 divisions:
a blocking force landing at Mito on the coast north of Toyko
and move west to establish a position north of Tokyo.
the main force landing in Kashima Beach south of Choshi with a goal to
clear Chiba province including the east side of Tokyo Bay and build airfields
and land tank divisions
before moving across the Kanto plain to attack Tokyo from the east.
a southern landing at Sagami Bay 30 days later would take
Yokosuka naval base and move rapidly north to be west of Tokyo.
the three armies would then move on Tokyo.
A second plan, subject to further change, dispensed with
the northern force and was reduced by 2 divisions. This acknowledged that
redeployment from Europe was not going well -- two million
experienced veterens were being released and units were in disarray.
a landing was to be made on Kashima Beach east of Tokyo with 5 divisions
to clear Chiba province, cross the Boso peninsula to Tokyo Bay,
built land-based air bases under the cover of carrier aircraft, and
built up 9 infantry and 2 tank divisions including some redeployed from the
The major landing was to be made ten days later at Sagami Bay,
the outer part of Tokyo Bay, southwest of Tokyo with the goal to
take the naval base at Yokosuka and open Toyko Bay and build up to
8 infantry and 3 tank divisions.
Then both armies were to move on Tokyo at D+30.
The southern, Sagami force, was to move quickly
north behind the cities on Tokyo Bay with elements tasked
for the ports of Yokohama and Kawasaki,
while the main force continued north to be northwest of Tokyo.
Meanwhile the Navy would move into Tokyo Bay to
provide support from the south.
One corp is unaccounted for in the surviving drafts of the plan at the time of the surrender,
which shows that the planning was still in progress.
A third plan retained the three landings of 25 divisions with 1 paratroop division in reserve.
This was MacArthur's plan and assumed that more troops were available than the Joint Chiefs
Return to: WW2 Menu About this page: Downfall - Description of the plans for
the invasion of the home islands of Japan in the Fall and Spring of 1945-46.
Last updated on Jan 23, 2009 -- add Appendix
October 14, 2003 - add Troops.
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