Preparations for Invasion of Japan
Contributor: C. Peter Chen
ww2dbaseThe eventual successful development of the atomic weapons would play a role in the Japanese decision to surrender, but few had the knowledge of the existence of such a research program. Those who knew of its existence could only regard it as a wildcard of sorts, since success was far from being guaranteed. Therefore, the military campaign against Japan proceeded to prepare for an invasion of the Japanese home islands. By this time, Allied naval and air fleets were operating nearly unopposed, attacking targets of their choosing without facing significant opposition.
ww2dbaseOn 14 Jul 1945, battleships South Dakota, Indiana, and Massachusetts bombarded Kamaishi, Honshu; the primary target was the Kamaishi Works of the Japan Iron Company. A small Japanese gunboat attempted to defend against the overwhelming American force. The escorting destroyers moved forth to fire at the small craft; due to either the small size of the target or inaccurate American aiming, several destroyer shells flew over the target and exploded in the town, killing civilians and causing fires. As the battleships opened fire on the iron work facilities, smoke from the burning civilian buildings periodically provided a smoke screen for the Japanese. Nevertheless, when the bombardment was completed, Japanese officials estimated that the damage done to the plants required about 65% of the total value of the physical assets to repair, and the repair would take 8 to 12 months to complete. Explosions at the iron works facilities killed many civilians, while nearby refrigeration and fishing industries were also damaged.
ww2dbaseOn 15 Jul, three Iowa-class battleships Iowa, Missouri, and Wisconsin bombarded industrial targets at Muroran, Hokkaido. The targets were the Wanishi Iron Works plants and the Muroran Works, both of the Japan Steel Company. Despite limited visibility, the successful bombardment caused damages amounting to the loss of about two and a half months of output of coke and a slightly smaller loss of pig iron for the Wanishi Iron Works, and 40% of a month's output for the Muroran Works. The bombardment also significantly disrupted railway, electric, and telephone systems.
ww2dbaseOn 17 Jul, battleships shelled Hitachi with a stunning count of 1,207 16-inch shells and 292 6-inch shells from light cruisers.
ww2dbase18 Jul, the North Carolina, Alabama, Iowa, Missouri, and Wisconsin of the US Navy and King George V of the British Navy bombarded Hitachi and surrounding areas, Honshu. Gunfire moderately damaged the Taga Works and Mito Works of Hitachi Manufacturing Company. The Yamate Plant and the copper refining plants of Hitachi Mine also received damages. Civilian targets were also bombarded, causing significant damage to housing sections as well as telephone, power, and water services. Fires spread quickly due to the lack of firefighters (already fled the city).
ww2dbaseOn 29 and 30 Jul, South Dakota, Indiana, Massachusetts bombarded Hamamatsu, Honshu, during the night. During this bombardment, high explosive and incendiary shells were used, causing widespread damage.
ww2dbaseOn 9 Aug, a day after the second atomic bomb was dropped on Nagasaki, South Dakota, Indiana, and Massachusetts conducted a second bombardment on Kamaishi, Honshu, destroying what was left from the first bombardment three weeks prior. Tally of shells fired would result to 850 16-inch shells from battleships, 1,440 8-inch shells from heavy cruisers, and a staggering 2,500 5-inch shells from supporting destroyers. If Akabane's observations in Jul were wrong, any remaining faith in Japan's ability to defend itself was crushed by Aug 1945.
ww2dbaseOverall, during this period Allied ships fired 4,500 shells from battleships' primary weapons alone.
ww2dbaseAs early as late 1944, American bombers began a bombing campaign against Japanese cities that killed as many as 500,000 by the end of the Pacific War. For more information on these bombings, please see the WW2DB article Bombing of Tokyo and Other Cities.
ww2dbaseOn 24 and 28 Jul, 1945, Task Force 38 under Admiral Halsey launched two carrier aircraft attacks against what was left of the Japanese fleet, which by now were confined to their home ports due to the combination of the lack of fuel as well as the near-total Allied air superiority. Most of the vessels were destroyed without being able to get underway, and marked the final destruction of the once proud fleet.
ww2dbaseEffect on Japanese Morale
ww2dbaseBetween the naval blockades and aerial bombings, however willing to fight for their home islands, the Japanese morale was being shaken. Yutaka Akabane, a senior level civil servant, observed:
ww2dbaseThe Invasion Plans
ww2dbaseAs the naval and air forces bombarded Japan, the Allied leaders planned the actual invasion, which was code named Operation Downfall. The responsibility of planning went to Douglas MacArthur, Chester Nimitz, George Marshall, Ernest King, Hap Arnold, and William Leahy. The inter-service rivalry between the US Army and US Navy was addressed by an agreement that, should situation deem necessary, US Army General Douglas MacArthur would assume total command. Regarding the Japanese capacity to defend the Japanese home islands, American planning assumed:
- "That operations in this area will be opposed not only by the available organized military forces of the Empire, but also by a fanatically hostile population."
- "That approximately three (3) hostile divisions will be disposed in Southern KYUSHU and an additional three (3) in Northern KYUSHU at initiation of the OLYMPIC operation."
- "That total hostile forces committed against KYUSHU operations will not exceed eight (8) to ten (10) divisions and that this level will be speedily attained."
- "That approximately twenty-one (21) hostile divisions, including depot divisions, will be on HONSHU at initiation of that operation Coronet and that fourteen (14) of these divisions may be employed in the KANTO PLAIN area."
- "That the enemy may withdraw his land-based air forces to the Asiatic Mainland for protection from our neutralizing attacks. That under such circumstances he can possibly amass from 2,000 to 2,500 planes in that area by exercise of rigid economy, and that this force can operate against KYUSHU landings by staging through homeland fields."
ww2dbaseThe invasion plan called for two separate invasions.
ww2dbaseOperation Olympic was the sub-plan that targeted the Japanese home island of Kyushu. It was scheduled to take place on 1 Nov 1945, code named X-Day, with Okinawa acting as the primary staging area. The invasion fleet was to include 42 aircraft carriers, 24 battleships, and over 400 destroyers and destroyer escorts. The fleet would escort 14 American divisions, both Army and Marine Corps, that would form the initial assault force. The American forces were to conquer and hold the southern third of Kyushu. A deceptive operation, Operation Pastel, was to be launched against cities on the Chinese coast and Taiwan in support of Operation Olympic.
ww2dbaseOperation Coronet was to take place on 1 Mar 1946, code named Y-Day, assuming Operation Olympic had successfully secured airfields so that additional land-based air support would be available. It was to be the largest amphibious operation in history, with 25 divisions participating in the initial invasion, including those in floating reserve; the great invasion force was to include those transferred from the recently-concluded European War. The invasion beaches were to be at Kujikuri on the Boso Peninsula and Hiratsuka at Sagami Bay, and the forces would work their way north across the Kanto plain toward Tokyo.
ww2dbaseBecause Japanese geography did not provide many invasion beaches, the Japanese organized a strong defense, particularly at Kyushu. Over 10,000 aircraft of various types and sizes were prepared as kamikaze aircraft. Underground networks of bunkers and caves stored food, water, and thousands of tons of ammunition. 2,350,000 regular soldiers and 250,000 garrison troops were deployed, 900,000 of which were stationed in Kyushu by Aug 1945. 32,000,000 militia, in other words all males between the age of 15 and 60 and all females between 17 and 45, were given the task to supplement the regular military; their weapons include everything from antique bronze cannons to Arisaka rifles, from bamboo spears to Model 99 light machine guns. Perhaps the eeriest fact was that after the war the United States discovered even children were trained to become suicide bombers when necessarily, strapping explosives around their torsos and rolling under the treads of American tanks. "This was the enemy the Pentagon had learned to fear and hate", said Dan van der Vat, "a country of fanatics dedicated to hara-kiri, determined to slay as many invaders as possible as they went down fighting". Although there was a strong dovish movement in Tokyo to end the war by seeking a conditional surrender, Ketsu-Go (Operation "Decision") continued to move forth, aiming to cause as much casualty as possible in order to sway American popular opinion. If they could cause more casualties than what the American people could accept, they thought, Japan might have a chance at negotiating for an armistice.
ww2dbaseNaturally, the American plan considered Japanese resistance. It noted the possibility that the invasion "will be opposed not only by the available organized military forces of the Empire, but also by a fanatically hostile population", which would result in high casualties. In a study done by the United States Joint Chiefs of Staff in Apr 1945, at least 456,000 casualties were to be expected for Operation Olympic alone. Some other evaluations were also done, and their casualty estimates ranged anywhere from 30,000 to 1,000,000. In preparation, the United States manufactured 500,000 Purple Heart medals to award to those injured in combat.
ww2dbaseOperation Downfall was never carried out. With the use of the atomic bombs and Russia's sudden declaration of war on Japan, WW2 in Asia ended without the need for the potentially costly invasion. At the date of this writing, over 100,000 of the Purple Heart medals still sat in American government warehouses.
ww2dbaseSources: American Caesar, Nihon Kaigun, Operational Experiences of Fast Battleships, the Pacific Campaign, Wikipedia.
Last Major Update: Mar 2008
Preparations for Invasion of Japan Interactive Map
Preparations for Invasion of Japan Timeline
|15 Apr 1945||American carrier aircraft struck Japanese airfields in southern Kyushu, Japan while 300 US Army B-29 bombers conducted raids on Kawasaki and Tokyo.|
|25 May 1945||Operation Olympic, the invasion of Japan, was approved by the US Joint Chiefs of Staff, setting the date at 1 Nov 1945.|
|2 Jun 1945||American carrier aircraft of Task Force 38 attacked airfields in southern Kyushu, Japan. On the same day, 12 Japanese ships were sunk or damaged by naval mines in Japanese waters.|
|3 Jun 1945||American carrier aircraft of Task Force 38 attacked airfields in southern Kyushu, Japan for the second day in a row. On the same day, 7 Japanese ships were sunk or damaged by naval mines in Japanese waters.|
|8 Jul 1945||Over 100 American fighters struck eastern Honshu, Japan from their bases on Iwo Jima, Japan.|
|10 Jul 1945||USS Yorktown (Essex-class) arrived off the coast of Japan and launched air strikes on the Tokyo area.|
|12 Jul 1945||A number of B-25 bombers based in Okinawa attacked military airfields on Kyushu, Japan.|
|13 Jul 1945||USS Yorktown (Essex-class) launched strikes on the northernmost Japanese island of Hokkaido.|
|14 Jul 1945||American battleships USS South Dakota, USS Indiana, and USS Massachusetts and escorting destroyers bombarded Kamaishi, Honshu, Japan; the primary target was the Kamaishi Works of the Japan Iron Company, but several destroyers shells overshot the target and hit the town, killing many civilians; battleship shells were more accurate, destroying about 65% of the industrial complex, but they also killed many civilians; this was the first time the Japanese home islands were subjected to naval bombardment. To the north, the sinking of 6 warships and 37 steamers on the ferry route between Honshu and Hokkaido effectively cut off the latter from the rest of the home islands. At Kure, aircraft of US Navy TF 38 damaged carrier Amagi, carrier Katsuragi, and battleship Haruna. Far to the south, the USAAF XXI Bomber Command canceled a long-range P-51 raid from Iwo Jima to attack Meiji and Kagamigahara near Nagoya due to poor weather.|
|14 Jul 1945||USS Yorktown (Essex-class) launched strikes on the northernmost Japanese island of Hokkaido.|
|15 Jul 1945||American battleships USS Iowa, USS Missouri, and USS Wisconsin bombarded industrial targets at Muroran, Hokkaido, Japan; the main targets were Wanishi Iron Works plants and the Muroran Works. From the air, American naval aircraft attacked northern Honshu and Hokkaido, destroying railways and coal ferries. 104 US Army P-51 fighters based in Iwo Jima Meiji, Kagamigahara, Kowa, Akenogahara, Nagoya, and Suzuko, Japan. B-24 bombers attacked Tomitaka, Usa, Kikaiga-shima, Amami Islands, Yaku-shima, Osumi Islands, and Tamega Island. After sun down, American B-29 bombers mined Japanese waters at Naoetsu and Niigata and Korean waters at Najin, Busan, and Wonsan, while other B-29 bombers attacked and seriously damaged the Nippon Oil Company facilities at Kudamatsu in southwestern Japan.|
|15 Jul 1945||USS Yorktown (Essex-class) launched strikes on the northernmost Japanese island of Hokkaido.|
|17 Jul 1945||UK Task Force 37 and US Task Force 38.2 launched their first strike on the Japanese home islands; it was the first British attack on Japan in the Pacific War. British Seafire carrier fighters were launched against Japanese airfields at Kionoke, Naruto, and Miyakawa. American warships bombarded Hitachi, Ibaraki Prefecture, Japan. 1,207 16-inch shells from battleships and 292 6-inch shells from cruisers were fired.|
|18 Jul 1945||American battleships USS North Carolina, USS Alabama, USS Iowa, USS Missouri, and USS Wisconsin and British battleship HMS King George V bombarded Hitachi, Ibaraki Prefecture, Japan with 2,000 shells; the Taga Works and Mito Works of Hitachi Manufacturing Company were moderately damaged, and the Yamate Plant and the copper refining plants of Hitachi Mine were lightly damaged. Civilian housing areas were also attacked, causing many deaths.|
|18 Jul 1945||American naval land-based aircraft attacked targets off Kawajiri and Tsushima Island, Japan; the 1,368-ton merchant steamer Chishima Maru and the cargo steamers Tagami Maru and Shintai Maru were sunk.|
|18 Jul 1945||Escort destroyer Yaezakura, construction not yet completed and had been abandoned since the previous month, was destroyed in a US Navy raid on Yokosuka, Japan.|
|18 Jul 1945||Kasuga capsized in her mooring during a US Navy raid on Yokosuka, Japan.|
|18 Jul 1945||Submarine chaser Harushima and auxiliary patrol vessels Pa No. 37, Pa No. 110, and Pa. No 122 were sunk by US Navy aircraft in the Yokosuka, Japan area.|
|18 Jul 1945||USS Yorktown (Essex-class) launched raids on the Tokyo area.|
|19 Jul 1945||US Navy Task Force 38 carrier aircraft damaged carrier Amagi, carrier Katsuragi, and battleship Haruna at Kure Naval Shipyard, Japan.|
|19 Jul 1945||US warships of Task Group 35.4 conducted a final bombardment of radar stations at Nojima Saki about 90 kilometers south of Tokyo, Japan.|
|20 Jul 1945||HMS Indefatigable joined UK Task Force 37 and US Task Force 38.2 for an attack on the Japanese home islands. On the same day, an US Army B-29 bomber failed to attack the Imperial Palace in Tokyo with a large "Pumpkin" bomb.|
|24 Jul 1945||British TF 37 launched 416 sorties, 261 of which were sent against the Japanese home islands and 155 were for defensive patrols; escort carrier Kaiyo was damaged by British carrier planes. On the same day, American TF 38 launched 600 aircraft against Kure, Nagoya, Osaka, and Miho, sinking battleship-carrier Hyuga, heavy cruiser Tone, and target ship Settsu, and damaging carrier Ryuho, carrier Amagi, battleship-carrier Ise, battleship Haruna, heavy cruiser Aoba, light cruiser Oyodo, transport Kiyokawa Maru; the Aichi aircraft factories at Nagoya were seriously damaged.|
|24 Jul 1945||Settsu was attacked by 30 US Navy F6F-3 fighters while off Kure, Hiroshima, Japan after 1500 hours, suffering one direct bomb hit and five near misses. Captain Masanao Ofuji grounded her on the island of Etajima to prevent sinking.|
|24 Jul 1945||USS Yorktown (Essex-class) and TF58 pounded shipping and installations around the Kure naval base.|
|25 Jul 1945||US carrier aircraft attacked Japanese shipping in the Inland Sea near Osaka and Nagoya, Japan.|
|25 Jul 1945||USS Yorktown (Essex-class) and TF58 pounded shipping and installations around the Kure naval base.|
|27 Jul 1945||A mine laid by USAAF B-29 aircraft sank the 1,025-ton Japanese army cargo ship Unten Maru in the in the western portion of the Inland Sea of Japan.|
|27 Jul 1945||A mine laid by USAAF B-29 aircraft sank the 887-ton Japanese merchant cargo ship Meiko Maru off Kogushi, Shimonoseki, Yamaguchi Prefecture, Japan.|
|27 Jul 1945||A mine laid by USAAF B-29 aircraft sank the Japanese merchant cargo ship Banshu Maru No. 55 in Odo Strait, Shimonoseki, Yamaguchi Prefecture, Japan.|
|27 Jul 1945||US aircraft damaged the Japanese merchant cargo ship Rokuzan Maru off the southeast coast of Korea.|
|27 Jul 1945||USAAF B-25 and P-51 aircraft on anti-shipping sweep off the southeast coast of Korea sank the 886-ton Japanese tanker Yushin Maru.|
|27 Jul 1945||USS Yorktown (Essex-class) and TF58 pounded shipping and installations around the Kure naval base.|
|28 Jul 1945||137 American P-47 aircraft based in Ie Shima, Okinawa, Japan attacked targest in Kyushu, Japan. On the same day, 471 B-29 bombers attacked smaller Japanese cities in the home islands with incendiary bombs. Finally, from the sea, US Navy TF 38 struck Inland Sea between Nagoya and northern Kyushu, sinking battleship Haruna, battleship-carrier Ise, heavy cruiser Aoba, and light cruiser Oyodo, and damaging carrier Katsuragi and carrier Hosho.|
|28 Jul 1945||US carrier aircraft attacked Ise at Kure, Japan, scoring 18 hits and many near misses, sinking her in shallow water.|
|28 Jul 1945||USS Yorktown (Essex-class) and TF58 pounded shipping and installations around the Kure naval base.|
|28 Jul 1945||While beached on the island of Etajima, Hiroshima, Japan, Settsu was attacked by 3 US Navy carrier aircraft, suffering two direct bomb hits.|
|29 Jul 1945||American battleships USS South Dakota, USS Indiana, and USS Massachusetts began a two-day bombardment of Hamamatsu, Shizuoka Prefecture, Japan.|
|29 Jul 1945||USS Yorktown (Essex-class) launched raids on the Tokyo area.|
|30 Jul 1945||American battleships USS South Dakota, USS Indiana, and USS Massachusetts ended a two-day bombardment of Hamamatsu, Shizuoka Prefecture, Japan. Meanwhile, carrier fighters attacked airfields, railroads, and tactical targets in the Kobe-Osaka region.|
|30 Jul 1945||USS Yorktown (Essex-class) launched raids on the Tokyo area.|
|4 Aug 1945||In a public statement, Douglas MacArthur announced that "a mighty invasion force is being forged", referring to the seemingly impending invasion of the Japanese home islands.|
|8 Aug 1945||USS Yorktown (Essex-class) launched raids on northern Honshu and southern Hokkaido, Japan.|
|9 Aug 1945||258 British Avenger, Corsair, Hellcat, Firefly, and Seafire carrier aircraft of Task Force 37 expended more than 120 tons of bombs and cannon shells on targets in and near the Japanese home islands. Meanwhile, American battleships USS South Dakota, USS Indiana, and USS Massachusetts bombarded Kamaishi, Iwate, Japan. 850 16-inch shells from battleships, 1,440 8-inch shells from cruisers, and 2,500 5-inch shells from destroyers were fired.|
|9 Aug 1945||USS Yorktown (Essex-class) launched raids on northern Honshu and southern Hokkaido, Japan.|
|10 Aug 1945||USS Yorktown (Essex-class) launched raids on Tokyo, Japan.|
|13 Aug 1945||USS Yorktown (Essex-class) launched raids on Tokyo, Japan.|
|1 Nov 1945||This date was the scheduled launch day for Operation Olympic, the invasion of Kyushu, Japan, which never took place.|
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James Forrestal, Secretary of the Navy, 23 Feb 1945