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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.

ww2dbaseNaval Bombardments

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.

ww2dbaseAerial Attacks

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:

"It was the raids on the medium and smaller cities which had the worst effect and really brought home to the people the experience of bombing and a demoralization of faith in the outcome of the war.... It was bad enough in so large a city as Tokyo, but much worse in the smaller cities, where most of the city would be wiped out. Through May and June the spirit of the people was crushed. (When B-29s dropped propaganda pamphlets) the morale of the people sank terrifically, reaching a low point in July, at which time there was no longer hope of victory or draw but merely desire for ending the war."

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

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