© 2007-2018 Bob Hackett and
Sander Kingsepp
Revision 1
SENSUIKAN!
Midget Submarines in Japan
and 'Operation Downfall' - 1945
1 March 1945:
The Second Special Attack Force (former First Special Base
Unit) for Kaiten attacks
is formed at Hikari, Yamaguchi Prefecture. Rear Admiral Nagai Mitsuru (former CO
of JUNYO) is appointed the CO. On that same day, a Kaiten crew training unit is
formed at Hirao, SE of Hikari.
20 March 1945:
The First Special Attack Force (planned strength 36
Kairyu type midget submarines and 8 Kaiten type human torpedoes) is formed on
Jogashima island, Kanagawa Prefecture. Rear Admiral Obayashi Sueo (former CO of
ZUIHO) is appointed the CO. The Tenth Special Attack Force is formed at Kure and
directly attached to Combined Fleet HQ. Rear Admiral Owada Noboru (former CO of
YAMASHIRO) is appointed CO.
The Tenth Special Attack Force, comprising submarine HA-109 and 12 Koryu
midget submarines, is tasked with developing new tactics for future Koryu
and Kairyu attacks.
In case of an Allied landing, it is to deploy to the landing area immediately to
support the local special attack force in actions against the invasion fleet.
April-June 1945:
Submarines I-156, I-157, I-158, I-159 and I-162
are tasked to transport kaiten human torpedoes to various bases.
7 May 1945:
The Fourth Special Attack Unit (24 Kairyus and 4 Kaitens)
is formed at Owase harbor, Mie Prefecture. Rear Admiral Mito Hisashi (former CO
of KATORI) is appointed CO. His headquarters are located at Toba, Mie
Prefecture, and his flagship is former submarine tender KOMAHASHI.
10 May 1945:
The Fifth Special Attack Unit is formed at Kagoshima,
Kyushu. Rear Admiral Komazawa Katsumi (former CO of NISSHIN) is appointed CO.
20 May 1945:
The Third Special Attack Unit is formed at Sasebo for
Koryu type midget and Shinyo exploding motor boat attacks. Rear Admiral Shibuya
Kiyomi (former CO of NAGATO) is appointed the CO.
25 May 1945:
The Joint Chiefs of Staff issue a directive to five-star
Generals of the Army Douglas MacArthur, Henry H. Arnold and Fleet Admiral
Chester Nimitz to proceed with the invasion of Japan.[1][2]
World War II Joint Chiefs of Staff
(National Archives)
28 May 1945:
The Kaiten human torpedo is formally adopted into
service.
Operation "Downfall" is the two-phase plan for the invasion of Japan.
With the exception of a part of the British Pacific Fleet, Operation "Downfall"
will be an American operation. On 1 November 1945, an amphibious assault,
code-named Operation "Olympic", will begin on the southernmost home island of
Kyushu, followed about 1 March 1946 by Operation "Coronet", the invasion of the
main island of Honshu.
The naval armada for Operation Olympic will be the largest ever
assembled. For the first time, the Third and Fifth Fleets will operate
simultaneously. The Third Fleet, under Admiral (later Fleet Admiral) William F.
Halsey, will be composed of 22 fleet carriers, 10 light carriers, 10 fast
battleships plus cruisers and destroyers. Halsey's carriers will provide about
1,900 aircraft. The Fifth Fleet, under Admiral Raymond A. Spruance, will have
over 20 carriers, 13 slow battleships, 20 cruisers plus destroyers and support
ships or about 800 warships and about 1,500 transports will carry the invasion
troops.
The Americans will assault Kyushu at three points. Four American Corps
consisting of 11 Army and three Marine divisions of General Walter Krueger's VI
Army are scheduled to take part in the initial landings. Once the southern third
of the island has been seized for use as a staging point, naval and air bases
will be established to support the next phase, Operation "Coronet", the invasion
of the Tokyo Plain.
General George C. Kenney's Far Eastern Air Force will commit 10 fighter
groups, 14 bomb groups, three reconnaissance groups and three night fighter
squadrons.
Operation Downfall, 1945-1946
(U.S. Army)
"Ketsu-Go"(Decisive Operation) is the Japanese plan for defeating the
Allied invasion. Since the only beaches suitable for amphibious assaults are on
Kyushu and the Kanto plain, south of Tokyo, Japanese intelligence correctly
predicts the invasion will take place in southern Kyushu at Miyazaki, Ariake Bay
and the Satsuma Peninsula.
The American landings at Kyushu will be opposed by 14 Japanese divisons,
seven independent mixed brigades, three tank brigades and thousands of men of
the Special Naval Landing Forces. These and other formations based on western
Honshu and Shikoku come under the Second General Army commanded by Field Marshal
Hata Shunroku, headquartered at Hiroshima Castle. On Kyushu alone, 790,000
mostly well dug-in Japanese with pre-registered weapons will oppose 550,000
American invaders.
Invasion Beaches on Kyushu
1 June 1945:
The Sixth Special Attack Unit is formed at Tanabe harbor,
Wakayama Prefecture. Rear Admiral Yokoi Tadao (former CO of CHIYODA) is
appointed the CO.
21 June 1945:
At 1700, Okinawa is declared secure.
24 June 1945:
The 20th Air Force's 313th Bomb Wing mines and bombs
Fukuoka, Karatsu, Sakai and Niigata harbors. Hikari Bay, Yamaguchi Prefecture.
DesDiv 52's destroyer NASHI, converted into a kaiten carrier, is repeatedly
near-missed by bombs or mines.
11 July 1945:
Hikari Bay. NASHI acts as a target for the
kaiten-carrying submarine I-157.
19-25 July 1945:
Hikari Bay. I-36 conducts several kaiten training
launches against NASHI operating as a target. On 25 July, a Kaiten piloted by
Ens Wada Minoru is lost during training and Wada is killed.
July 1945:
The Japanese Army and Navy air forces have more than 12,500
aircraft of all types available to defend their homeland. More are to be
available by the 1 November date set for the invasion. The Japanese plan to
coordinate their kamikaze and conventional air strikes with attacks from their
remaining conventional submarines, beginning when the invasion fleet is about 10
miles off Kyushu. The submarines will launch Kaiten suicide torpedoes to stop as
many transports as possible.
About 2,000 IJA and IJN fighters will engage the Americans and gain air
superiority over Kyushu. Another 300 or more IJN aircraft will attack the task
force and keep it from protecting the troop transports. Meanwhile, another 800
or so kamikaze will crash their planes into the American transports. As the
invasion armada grows closer, submarine attacks will intensify and another 2,000
kamikaze will attack in waves of 200 to 300. The Japanese estimate that the
kamikazes will sink over 400 ships and perhaps destroy a third to a half of the
invasion force before it lands.
KORYU Type D Midgets at Kure at War's End.
(U.S. Navy
Photo)
The IJN have few remaining warships left and little fuel. They still have
some fleet submarines, but between April and June 1945, of 248 Kaiten suicide
torpedoes ordered only 158 are produced. Instead of 300 smaller Kairyu
submersibles, only 125 are built and instead of 110 Koryu midget submarines only
44 were produced.
In the case of the Kaitens and Kairyus, the Naval General Staff expects a
33 percent hit rate, 66 percent for Koryus and 10 per cent for Shinyo manned
explosive motor boats. The five-man Koryu midget submarines will be employed
with either two torpedoes or an explosive charge in the suicide role. The IJN
plans to have 540 Koryu in service by the time of the invasion.
KAIRYU Hideaway
(National Archives)
The two-man Kairyu is armed with either two torpedoes or an explosive
charge. Most Kairyu are based at Yokosuka and inlets on the southern tip of the
Miura peninsula. By the fall of 1945, approximately 740 Kairyu are planned to be
deployed for home island defense in concealed bases in Kyushu and Shikoku, but
Allied bombing reduces considerably the number of midget submarines that will be
available.
24 July 1945:
Potsdam, Germany, near Berlin. President Harry S.
Truman, Soviet Premier Josef Stalin and British Prime Minister Clement Atlee
attend the Potsdam Conference to discuss post-war Europe. Separately, Truman
approves the plan for the invasion of Japan.
That same day, Rear Admiral J. Cary Jones, Jr.'s TG 35.3's USS PASADENA
(CL-65), SPRINGFIELD (CL-66), ASTORIA (CL-90) and WILKES-BARRE (CL-103) and six
destroyers from DesRon 53 conduct a high-speed anti-shipping sweep across Kii
Suido channel. The Fourth Special Attack Unit at Owase is ordered to stand-by to
intercept TG 53.3's cruisers.
25 July 1945:
Potsdam. The President orders the commencement of atomic
attacks on Japan as soon as possible.
Kushimoto, Wakayama Prefecture. TG 35.3 shells an IJNAF seaplane base and
airfield. Around 0600, twelve aircraft from TF 38 appear over Owase to attack
targets of opportunity. Subsequent attacks continue until 1455. Between 0600 and
1457, KOMAHASHI and kaibokan CD-45 (the latter converted into a Shinyo type
exploding motor boat tender) are subjected to successive air attacks and finally
grounded off Owase. CD-45 loses 30 hands KIA and 19 wounded.
26 July 1945:
Potsdam. The Allies (United States, United Kingdom and
China) broadcast the "Potsdam Declaration" that calls for the unconditional
surrender of Japan, or the alternative of its prompt and "utter destruction".
[3]
Jogashima Island. Around 0900, a lone B-24 (or a PB4Y Privateer) strafes
the island and drops five bombs. One Kairyu of Rear Admiral Obayashi's First
Special Attack Force is slightly damaged by the strafing. 11th AF Consolidated
B-24 “Liberators” attack the Kataoka naval base.
The First Special Attack Unit detachment stationed at Ajiro harbor,
Shizuoka Prefecture (12 Kairyu type midget submarines) sustains loss of one
submarine.
30 July 1945:
TF 38 aircraft conduct a sweep against Japanese shipping
in Maizuru Bay. Ajiro harbor, Shizuoka Prefecture. Between 1100 and 1300 some
sixty carrier planes raid the area. Three midget submarines of the First Special
Attack Unit detachment (11 Kairyu type midgets) are damaged, one sailor is
killed.
28 July 1945:
Tokyo. Prime Minister Admiral, the Baron, Suzuki
Kantaro (14)(former CO of TSUKUBA) announces that Japan will ignore the Potsdam
Declaration.
30 July 1945:
TF 38 aircraft conduct a sweep against shipping in
Maizuru Bay. Between 1100 and 1300, some sixty carrier planes raid Ajiro harbor,
Shizuoka Prefecture. Three midget submarines of the First Special Attack Unit
detachment (11 Kairyu type midgets) are damaged and one sailor is KIA.
Early August 1945:
The Shimoda detachment of the First Special Attack
Force (12 Kairyu type midgets) receives a report about the sighting of an
American submarine shelling Mikimoto lighthouse, off Shimoda harbor. A Kairyu is
diespatched to intercept the submarine, but fails to locate it.
6 August 1945:
At 0815, Colonel (later Brig Gen) Paul W. Tibbetts'
B-29 "Superfortress", nicknamed "ENOLA GAY", of the 509th Composite Group, drops
the 15-kiloton yield "Little Boy" uranium atomic bomb on Hiroshima.
Colonel Tibbetts with B-29 ENOLA GAY
That same day, following TG 35.3's bombardment of Kushimoto, four Kaitens
are deployed from Otsujima base to Tanabe to be attached to the Sixth Special
Attack Unit.
8 August 1945:
Moscow declares that from 9 August 1945, the Soviet
Government will consider itself to be at war with Japan.
9 August 1945:
At 1101, Major (later Brig Gen, ANG) Charles W.
Sweeney's B-29 "BOCKSCAR", of the 509th Composite Group's 393rd Bomb Squadron,
drops the 21-kiloton yield "Fat Man" plutonium atomic bomb, on Nagasaki.[4]
That same day, carrying out Stalin's pledge at Yalta, Marshal Aleksandr
Vasilevsky, CINC, Soviet Far East Forces, launches Operation "August Storm", the
invasion of Japanese-held Manchuria (Manchukuo). The attack is made by three
Soviet army groups ("fronts") comprising 80 divisions of 1.5 million men. In
less than two weeks, the Soviets defeat General Yamada Otsuzo's depleted and
ill-equipped Kwantung Army of over 600,000 men.[5]
10 August 1945:
Japan offers to surrender to the Allies, if Emperor
Hirohito (Showa) is allowed to remain the nominal head of state.
12 August 1945:
The United States announces it will accept the
Japanese surrender and that the emperor can remain in a ceremonial capacity.
Shikoku, Kochi Prefecture. That same evening, the Suzaki kaiten
detachment of the Eighth Special Attack Unit receives a report about the
sighting of an enemy task force off Shionomisaki, Wakayama Prefecture. Based on
that information the local IJA commander expects a landing at Tosa Bay the next
morning. Two kaitens are immediately dispatched to Tosa Bay and sortie at 0600
the next morning, but fail to locate the enemy and return by 1000.
13 August 1945:
Tokyo. At an evening conference attended by General
Umezu Yoshijiro, Chief of the Army General Staff and Admiral Toyoda Soemu (33),
(former CO of HYUGA), Chief of the Navy General Staff, the Vice Chief of the
NGS, wild-eyed Vice Admiral Onishi Takijiro (40)(former XO of KAGA) proposes
"that if we are willing to sacrifice 20 million Japanese lives in special
attacks (kamikaze), victory can still be achieved!"
14 August 1945:
Tokyo. At 1020, the emperor convenes a conference of
his most senior military officers. Field Marshall Hata, freshly arrived from
Hiroshima, expresses no confidence in Japan continuing the war over appeals from
such strong-willed, arrogant personalities as Field Marshal Sugiyama Hajime and
Fleet Admiral Nagano Osami who exhibit a dull-witted state of denial. The
emperor dismisses their protestations for protracted carnage.
The emperor notes that with the Soviet entry into the Pacific War and the
enemy's use of atomic weapons, not even Onishi's Special Attack forces can stop
them. He requests that his senior officers cooperate with him to end the war.
Later, the Japanese announce that the emperor has decided to accept the Potsdam
Declaration's terms and end the War, effective the following day.
That same day, 167 B-29s of the 20th Air Force from Saipan bomb Hikari
Naval Arsenal, Yamaguchi Prefecture. The raid is supported by North American
P-51 "Mustang" fighters from Iwo Jima, attacking various targets in the same
area until 1040 in the morning. 71.8 percent of the arsenal's total roof area is
destroyed. 738 workers, mostly mobilized middle school students, die in the
attacks.
Emperor Hirohito Reads an Imperial Rescript
15 August 1945: Cessation of Hostilities:
Imperial Palace, Tokyo. At
noon, the emperor announces Japan's surrender that is broadcast by radio all
over the Japanese Empire.
Port Arthur, Manchuria. Lost to Japan in 1905, the Soviet Navy Flag
flies again on 22 August
18 August 1945:
The Red Army makes three amphibious landings in
northern Korea, one landing in Sakhalin and one at Shimushu, Kurile Islands.
Korea is subsequently divided at the 38th parallel into Soviet and U.S. zones.
After the surrender of the Kwantung Army in Manchuria, about 590,830 Japanese
are sent to PoW camps in Siberia. [6]
Surrender
(National Archives)
2 September 1945: Formal Surrender Ceremonies:
Tokyo Bay. Japanese
representatives arrive on board USS MISSOURI (BB-63) more than two weeks after
Japan accepted the Allies' terms. Foreign Minister Shigemitsu Mamoru and General
Umezu Yoshijiro, Chief of the Army General Staff are in the front row.
Witnessing the surrender on behalf of the IJN are Rear Admiral, the Baron,
Tomioka Sadatoshi (former CO of OYODO)(middle row, behind Umezu), Rear Admiral
Yokoyama Ichiro (former CO of KUMA)(back row, right) and Captain Shiba Katsuo
(former CO of OI) (back row, behind Tomioka). The others present are the
witnesses of the IJA and the Foreign Ministry. At about 0905, Shigemitsu and
Umezu sign the Instrument of Surrender, followed by General of the Army, Douglas
MacArthur, Supreme Commander for the Allied Forces, Fleet Admiral Chester A.
Nimitz, representing the United States, and eight representatives of the Allied
Forces.
At the time of surrender, 43 Kaiten torpedoes (mostly Type 1 or Type 1
Mod. 1) are located at Otsujima base, 52 at Hikari, 39 at Hirao, 37 at Kure
Naval Arsenal and 16 at Oga. All are destroyed or scuttled after the end of
hostilities. 224 Kairyu submersibles were built by the end of war plus another
207 were in various stages of completion. In addition to about 115 Koryus built
during the war, some 500 are found incomplete.
With the War's end, Operation "Downfall" is cancelled. General of the
Army George C. Marshall, CoS, U.S. Army, estimates up to one million casualties
for the invasion of Japan, but a contemporary Army study estimates the invasion
and subsequent Battle for Japan would have cost as many as four million American
casualties, including up to 800,000 fatalities, and five to ten million Japanese
fatalities.
If Downfall had become necessary and American forces were contested
heavily in southern Japan, the Soviets most probably would have secured Hokkaido
and invaded northern Honshu. This may have led to the vanquished nation's
partitioning into North and South Japan, as occurred in Korea and persists to
this day.
May 1978:
During the dredging works at Ajiro harbor, Shizuoka
Prefecture, the wreck of a scuttled (or sunken) Kairyu type midget submarine is
discovered. After restoration it is now displayed at Arashiyama Art Museum in
Kyoto.
August 1989:
The well-preserved hull of a Type 4 Kaiten is discovered
under one of the buildings of the Takeda Pharmaceutical Co. Ltd. located on the
premises of the former Hikari Naval Arsenal.
Authors' Notes:
[1] The Joint Chiefs of Staff, shown in 1943, are from left
to right: Gen Henry H. Arnold, CoS, U.S. Army Air Forces; Adm William D. Leahy,
Chairman, JCS; Adm Ernest J. King, Chief of Naval Operations and Gen George C.
Marshall, CoS, U.S. Army.
[2] Gen Arnold, in addition to being CoS of the Army Air Forces and a
member of the JCS, was the self-appointed commanding general of the USAAF's
Twentieth Air Force (B-29s).
[3] The Soviet Union was not a signatory to the Potsdam Declaration as
they were not at war with Japan at the time.
[4] Sweeney's primary target was the port city of Kokura on Kyushu;
however, it was obscured by smoke and haze, so Sweeney proceeded on to his
secondary target, Nagasaki.
[5] At the Yalta Conference, held 4-11 February 1945 in the Crimea (now
in Ukraine), between the US, UK and the Soviet Union, Premier Stalin agreed to
attack Japan within 90 days after the defeat of Germany. After the defeat of
Japan, the Kurile Islands and the southern part of Sakhalin ceded to Japan by
the Treaty of Portsmouth after the 1904-1905 Russo-Japanese War were returned to
the Soviet Union as agreed at Yalta.
[6] By 1950, 510,409 Japanese POWs were repatriated to Japan by the
Soviets.
Thanks for assistance go to Dr. Higuchi Tatsuhiro of Japan.
-Bob Hackett and Sander Kingsepp
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