What if the a‑Bomb Had Never Been Invented – and America Invaded Japan in 1945?

 In Japan

In the summer of 1945, U.S. lead­ers expect­ed one mil­lion American sol­diers would soon be dead or wound­ed.

Operation Downfall – the code­name for the pro­posed amphibi­ous inva­sion of Japan in 1945 – would have made the D‑Day inva­sion of Normandy look like a cake­walk. The first phase – Operation Olympic, sched­uled for November 1945 –  called for seiz­ing air­fields on the south­ern­most Japanese island of Kyushu. Those air­fields would have pro­vid­ed air cover for Operation Coronet, slated for March 1946, which would landed Allied troops on the main island Honshu, for an assault on Tokyo that hope­ful­ly would compel Japan to sur­ren­der.

In the end, Japan did sur­ren­der on August 15, after atomic weapons had been dropped on Hiroshima and Nagasaki, and the Soviet Union had declared war on Japan. But what if Japan hadn’t sur­ren­dered? What if the A‑bomb hadn’t been invent­ed, or Japan chose to fight on regard­less, and the Allies had storm Tokyo?

A com­put­er wargame sug­gests an inva­sion of Japan would have been a blood­bath.

Even in the summer of 1945, assault­ing Japan seemed a grim prospect. American sol­diers had suf­fered a forestate in the bloody inva­sions of Iwo Jima and Okinawa, where Japanese troops fought to the death rather than sur­ren­der. How much more fanat­i­cal would have been their defense of the sacred Japanese home­land, includ­ing thou­sands of kamikaze air­craft and boats that would have taken a heavy toll of Allies ships. Pentagon plan­ners warned that that Allied troops – mostly American, but sup­port­ed by British, Canadian, Australian and New Zealand con­tin­gents – could suffer up to one million casualties. Japanese mil­i­tary and civil­ian casu­al­ties would have been far heav­ier.

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But on August 6, 1945, a U.S. B‑29 bomber dropped an atomic bomb on Hiroshima, fol­lowed by anoth­er A‑bomb on Nagasaki on August 9. To the relief of many Americans and Japanese — includ­ing my late father-in-law, a B‑29 bom­bardier who would have flown air sup­port for Operation Olympic – Japan sur­ren­dered a few days later.

For decades, con­tro­ver­sy has sur­round­ed the deci­sion to drop The Bomb. The tra­di­tion­al nar­ra­tive has been that the atomic bombs spurred Japan to sur­ren­der, and spared mil­lions of American and Japanese. Revisionist his­to­ri­ans argue that the A‑bomb was unnec­es­sary and even immoral: Japan, already starv­ing from the Allied naval and air block­ade, would have sur­ren­dered anyway once the Soviet Union declared war on Japan. Or, that the mil­lion-casu­al­ty esti­mate was exag­ger­at­ed (for a good sum­ma­ry of the argu­ments pro and con, see this article by his­to­ri­an Alex Wellerstein).

Whichever argu­ment is right – or more likely both argu­ments are right —  his­to­ri­ans have tended to focus on high-level ques­tions of war and peace, diplo­ma­cy and weapons of mass destruc­tion. But what would an actual Allied inva­sion of Japan have looked like?

A clue can be found in Japan ’45, from John Tiller Software, a hobby wargame that depicts Operation Olympic (a sequel, Japan ’46, covers Operation Coronet). Japan ’45 is a bat­tal­ion-level sim­u­la­tion involv­ing thou­sands of U.S. Army and Marine, Japanese, British and French units maneu­ver­ing over a 2‑D map of Kyushu.

At first glance, the Allies appear to be an unstop­pable jug­ger­naut. They field a stag­ger­ing array of units, includ­ing tanks, armored cars, infantry (foot and mech­a­nized), para­troop­ers, com­man­dos, artillery (towed and self-pro­pelled) and anti-tank guns, backed by fight­ers, bombers, bat­tle­ships and destroy­ers. They enjoy far more fire­pow­er and mobil­i­ty than the Japanese, whose army is mostly a First World War-style force of foot infantry and artillery.

But the unstop­pable Allied war machine soon clanks to a halt. For starters, the ter­rain is not friend­ly to a mech­a­nized army. In Japan ’45, the map of Kyushu is stud­ded with rice pad­dies, forests, hills, vil­lages, rivers and streams. The ter­rain restricts move­ment to a crawl, and pro­vides nat­ur­al defen­sive cover for the defend­ers. Despite all those Allied Sherman tanks, there will be no dash­ing Patton-esque blitzkriegs on Kyushu.

And what nature can’t pro­vide, Japanese shov­els will. The inva­sion beach­es on Kyushu are stud­ded with mine­fields, trench­es, bunkers and pill­box­es. The Allied player can only gnash his teeth as bombs, napalm and one-ton shells from bat­tle­ships barely scratch Japanese troops embed­ded deep in their for­ti­fi­ca­tions.

Finally, there is the Japanese sol­dier to con­tend with. The core of the Imperial Army was its leg­en­dar­i­ly tough infantry, which could with­stand the hard­est pri­va­tions, and pre­ferred to fight hand-to-hand with the bay­o­net. Even if their weapons aren’t quite as good or plen­ti­ful as Allied equip­ment, they’re good enough to inflict mas­sive casu­al­ties on the invaders.

Playing Japan ’45, as the Allies against the AI-con­trolled Japanese side, graph­i­cal­ly demon­strates that Operation Olympic would have been a meat­grinder. U.S. Army and Marine assault troops splash­ing ashore suffer heavy losses from mine­fields, artillery and machine guns. Pinned down on the exposed beach­es, the rifle­men and engi­neers advance inch-by-inch. Eventually the Japanese are dis­lodged from their entrench­ments, and once in the open, they are vul­ner­a­ble to Allied air and naval fire­pow­er.

But then what? The ter­rain on Kyushu is too rough and restrict­ed to allow an Allied break­through. Once the Japanese defend­ers are pushed off the bushes, they just regroup inland among the hills and woods, and the Allies have to dig them out again.

The game sug­gests the inva­sion of Japan might have resem­bled the Okinawa campaign, where U.S. troops had to battle through mul­ti­ple Japanese defen­sive lines in a grind­ing battle of attri­tion that cost 50,000 American casu­al­ties – and 400 ships sunk or dam­aged by kamikazes – before Okinawa was con­quered. Like Okinawa, the ques­tion is not whether the Allies will cap­ture Kyushu, but what price they will pay for it.

Which is really what an inva­sion of Japan would have boiled down to. That Japan was being invad­ed at all was proof that the war was lost. As an island nation, Japan’s first line of defense was the Imperial navy and air force, and both of these were rust­ing on the bottom of the Pacific or in remote jun­gles.

Short of sur­ren­der, the best the Japanese could hope was a divine mir­a­cle (and in fact, a mas­sive typhoon in October 1945 would have badly dis­rupt­ed Allied inva­sion plans). Or, to inflict so many casu­al­ties as to induce the Allies to a nego­ti­at­ed peace. But after so many years of blood­shed, the Allied nations were in no mood to nego­ti­ate any­thing else than Japanese sur­ren­der.

In the end, Japan gave up before inva­sion was nec­es­sary. A fact for which many Americans and Japanese had cause to be thank­ful.

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