Sea Power
Desperate War of Japan in the Pacific
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 IJN battle plan in 1940
IJN had occupied German Truk in October 1914. As a result of Paris Peace Conference in 1919, Japan governed the Caroline Islands, the Marshall Islands and the Gilbert Islands. There were 1400 islands in the region. Could the islands were useful to defend Japan against the US? IJN changed a battle line of the Ogasawara Islands against USN as follow,
    1918----- Ogasawar Islands are patrol lines
    1919Jan18 Paris Peace Conference
    1920Aug10 IJA established a branch of fort building at Chichijima
    1921Jun10 IJA began building
    1922Feb06 IJA stopped building by Naval Disarmament Treaty
    1922Apl01 IJN pulled up troops
    1923----- Ogasawara Islands are final battle lines
    1923----- IJA established a fort head quater at Chichijima
    1927----- Fort Defense Guideline
    1933----- Built a north-south runstrip of 800x200m at Iwojima
    1936Mar25 IJN was responsible for Ogasawara Islands except for Chichijima by Fort Zone Law
    1937----- Built a east-west runstrip of 800x200m at Iwojima
    1939Apr-- IJN established a koukutai at Chichijima
    1939Nov15 IJN established the 4th fleet and changed a final battle line to the Marshall, the West Caroline
    1940Feb-- IJN changed imaginary combat sea into the Marshall

Chichijima Yohsai Kensetu jidai
Nichi-Doku senso

IJN built air bases at Saipan, Tinian, Ruote, Truk, Minami Torishima in the first of November 1941. Saipan and Tinian were able to deploy 48 fighters and 80 Nells . Palau, Taroa, Wotje and Ruote were 48 fighters and 144 Nells. Saipan, Truk, and Palau were able to deploy 24 flying sea boats. Wotje and Imeji were 34 and 36 flying sea boats each.
Morimoto, p178

The 4th Fleet of IJN increased aircraft of 36 Nells, 36 Claudes and 24 Mavises in September 1941. The 24 Mavises of Yokohama Air Group deployed Iemji in the Jaluit Atoll. The 36 Claudes of Chitose Air Group were deployed in Ruote, Taroa and Truk. An aircraft carrier transported the fighters to the islands. IJN built 3 airfields (Pagan, Saipan, Tinian) in the Mariana Islands, Peleiu in Palau and 3 airfields (Kwajalein, Wotje, Maloeap) in the Marshal Islands till then.
Chihaya jyoh, p177
Tainan ku no Ace
Yokohama Kokutai

A flight example of 3 Nells shows,

    Ruotto -1,764km-> Truk (stay at night) -1,079km-> Tinian (refuel) -1,166km-> Iwojima (stay at night) -1,198km-> Kisarazu
    Chuko Move to Roi-Namur

 Real war
I do not know why IJN advanced an imaginary battle line far to the Marshall Islands, considering logistics. IJA and IJN used 1.62 MGT and 1.81 MGT of merchant ships to supply them and continue operations in 1943. Japan had to live for civil 2.62 MGT. 3 MGT was necessary for Japanese people's life at least.
Ohi, p90

Island area [km2]
It seemed that Commander of GF Koga was afraid of US heavy bombers of B-17 or B-24 to reconnaissance or release bombs in staying at Truk, though battleships waited for a battle at the Marshall Islands.

Actually a battleships and some heavy cruisers ran to be sunk by submarines. IJN established the 8th fleet of heavy cruisers, though commander of Rabaul referred to no needs. I suppose the commander needed destroyers. IJN fought wrong. IJN big warships had better stay still like Germany or Italy. If a battleships ran, a few destroyers had to escort her from enemy submarines. IJN always troubled in short of destroyers.

Although IJN built air bases in the Marshall Islands for a final battle in 1943, USN destroyed each base for one day raid in Febrauary 1944. Without support of air force of carriers, the Marshall Islands were not almost useful for IJN. IJN had lost supeior sea power since the Midway battle in 1942. IJN should use the construction material to build airfields and positions in the Ogasawara Islands, the Mariana Islands, the Amami Islands and Okinawa. IJN lost 70% of carriers aviators in air battle of the Solomons Islands before the battle of the Marshall Islands. IJN worried few airfields in the Solomons and few aviators in the Marshall ironically. I list up voyage distances between major ports.

 Distance between airfields
Distances between islands
1943Aug15Attu to Kiska310km107°
1944Sep15Peleliu to Morotai857km50°
1944Oct20Peleliu to Tacloban 1,115km295°
1945Mar2tUlithi to Kerama 2,221km326°
The Pacific War was air battle how either Japan or US controlled the air and the sea in the Pacific. Warships could not run safe under enemy aircraft. Why could USN carriers task force often raid a harbor or an airfield easily? I do not know only one case that IJN could intercept a carrier-aircraft-raid plan near Rabaul. How IJN did land based aircraft or flying boats patrol the sea? I show IJN airfields and their airstrips to confirm a distance between 2 positions. Forexample, distance between Attu and Kiska is 305km. Fighters could cover the other island with their range if Japan could build an airfield at Kiska. But Japan had no potential or ability to construct in the north of the Pacific. Without air power of an aircraft carrier, Japan could not have these islands. Distance between Shumshu and Attu are 1,180km and azimuth 72°. It was hard for fighters to fly the round distance and combat considering the weather of the north Pacific. Some sites writes domestic airfields ( Himitsu Kichi, Hokkaido no Hikoujyo, Tokyo-to no Hikoujyo ) in Japanese.

USA and Marines landed on Morotai Island and Peleliu at the same time on 15 September 1944. P-38 fighters flew and from Biak to Leyte via Morotai. The P-38 advanced to Philippines. How far is between Morotai and Pelileu?

VPB-208 departed Ulithi Atoll for Kerama Rettoh Okinawa about midnight 31 March 1945. They flew 2,221km azimuth 326°

 USN turned to offensive otherwise no recovery of IJN air force
USN invaded the Solomons Islands step by step at first. Japan lost 95% of aircraft production yearly in Solomons and New guinea. In 1943, IJN and IJA lost 205% and 107%of aircraft production yearly. USN had planned to advance considering range 300nm of fighters in 1942. IJN lost air force power at the Solomons Islands in 1943, though IJN prepared air bases at the Marshall Islands ironically since 1940.

11 Betties were lost when 17 Betties intercepted a task force of USS Enterprise. The task force came near Rabaul on 21 February 1942. They were intercepted by F4F. The 6 remains were all incapable for the next operation.
Ikari, p152

When USN task force attacked the Truk Atoll by air raid on 17 February 1944, the task force left Majuro 5 days ago. The distance between Truk and Majuro is 2,180km. Therefore average speed was 10kt. The TF had 28 destroyers. While in case of Pearl Harbor attack by IJN, KB ran 3,500nm with 9 destroyers only. The average speed was 11kt. USN had confidence of carriers air defense system after the Truk raid.
Nimitz, p104

USAAF fighter's reconnaissance
P-38 flew over Truk regularly after IJN lost Saipan. The distance between Saipan and Truk is 1,090km. Otherwise a IJA fighter's pilot could not fly at the sea alone. IJA intended air combat against Russia in the final stage of the Pacific War.
Truk Islands I。。Saipan kanraku-goro made

 US invasion positions in Iceberg Operation
US built airfields for fighters at Iejima after Iceberg Operaion in 1945 at last. The distance between Iejima and Kanoya is 630km. This is half of Rabaul and Guadalcanal. And more the distance of Atsugi and Iwojima is 1220km. F4U-1D of US Marines MAG-31 took off CVEs 100 mile off Okinawa and landed Yomitan on April 7. MAG-33 landed Kadena on April 9. The distance between Iejima and Miyakojima was 285km. US stopped plan to occupy Oki-no-daito, Miyako, Kikai and Tokunosima on April 26. US was to build 18 and 2 airstrips in Okinawa and Iejima each. Only 2 airstrips were nearly finished at Yomitan and Iejima by the end of May. The first finished airstrip was 2,100m for medium bombers in Yomitan on June 17. Airsrips for fighters at Kin and Awase was built just before use by the end of June. USN occupied Kumejima for air warning radars on June 26. In the end of the Pacific War, USAAF had recieved 2,132 B-29s. USN had 99 carriers which were equipped with 4,250 aircraft. RN had 24 carriers which were equipped with 762 aircraft.
Okinawa, p100, p445-p447
F4U, p59
Chihaya, p55
米軍はIceberg作戦において,183,000人の兵員と747,000トンの物資を11の港から430隻の輸送艦貨物船に積み込んだ。補給のデポはEniwetok, Ulthi, Saipan と Leyte だった。沖縄戦で以下のような莫大な物資を補給した[1]
  1. Fuel oil  10,133,000 barrels
  2. Diesel  323,000 barrels
  3. Avgas  25,573,000 gallons
  4. Bombs and ammunition  16,375 tons
  5. Replacement aircraft  998
  6. Refrigerated provisions 2,219 tons
  7. Dry provisions 4,005 tons
  8. Ship's stores 575 tons
  9. Mail 15,398 bags
  10. Passengers 1,240
  11. Replacement aircrew  220
  12. Replacement personnel 1,032
USN bypassed 12 IJN air bases (Moen, Dublon, Param, Eten, Umani, Santawan, Ponape, Kusaie, Babelthuap, Nagesebus, Yap, Woleai) in the Caroline Islands, 5 air bases (Wotje, Taroa, Imeji , Mille, Greenwitch) in the Marshall Islands and Nauru in the Gilbert Islands after all. Although IJN air bases were not effective to defend the US invasion, IJA fought desperate ground combats in Iwojima and Okinawa and US ground forces had heavy damage since Japanese invasion of Philippines. USN reached at Okinawa again as Commdore Perry's campaign in 1853.

Japan deployed 276,000 troops in 25 islands. While US occupied 8 islands only and Japan lost 116,000 in the islands. Therefore 160,000 troops of Japan were isolated. 120,000 of then could return home after the War. So 40,000 troops died of hunger and illness. 148,000 troops lost 90% of them in New Guinea.[1]

Although IJN bureaucrats had studied battle against USN since 1920s, they did not think total war at all. On the other hand IJA bureaucrats had studied German total war in WWI. But IJA mistook Chinese nationalism. IJA had been weary of war in China since 1931. IJN ignored submarine warfare at logistics. When IJN bureaucrats found their mistakes in the Pacific War, they thought suicide attack. Considering US logistic power, Japan could not defend isolated islands, Okinawa in the Pacific.

[1] Hori, p117-118
[2] Logistics

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