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Why did the United States drop two nuclear bombs on the Japanese mainland? It appeared that Japan was ready to surrender.

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related (but closed): Were the atomic bombings of Hiroshima and Nagasaki necessary? –  tcrosley May 1 '12 at 21:20
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Part of the reason was to test the effects of such weapons. That's why they chose targets that were relatively untouched thus far. –  davidjwest May 2 '12 at 22:43
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@BrotherJack well by "deploying weapons in Japan" I fisrt think about placing the nuclear weapons on the vessels that were stationed in the Japanese ports against the USSR after the war. –  Anixx May 4 '12 at 3:45
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Probably preventing any significant Soviet occupation of Japan was also a big reason why the US wanted a quick surrender lending impetus to the decision to use the bomb –  Sid Jan 11 '13 at 2:01
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I do not think that by any stretch of the imagination was Japan "ready to surrender". All American pacific operations were met with fierce resistance which increased rather than diminished as they got closer to and started taking home islands. Even after both bombs had been dropped there was still significant resistance to surrender and it was only the direct and unprecedented intervention of Hirohito that changed the balance. Many Japanese would have preferred to see Japan destroyed rather than surrender. –  PurplePilot Sep 16 '13 at 19:12
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7 Answers

The official reason was to avoid a long and costly battle attempting to force the Japanese to surrender by invading the mainland. The Japanese were tenacious fighters and their tactics of Kamikaze suicide bombers and their courageous defense of their country in engagements such as the Battle of Okinawa, lend substantial credibility to this claim. Some such as General Eisenhower disagreed to as whether such a maneuver was really necessary.

"...in 1945... Secretary of War Stimson, visiting my headquarters in Germany, informed me that our government was preparing to drop an atomic bomb on Japan. I was one of those who felt that there were a number of cogent reasons to question the wisdom of such an act. ...the Secretary, upon giving me the news of the successful bomb test in New Mexico, and of the plan for using it, asked for my reaction, apparently expecting a vigorous assent.

"During his recitation of the relevant facts, I had been conscious of a feeling of depression and so I voiced to him my grave misgivings, first on the basis of my belief that Japan was already defeated and that dropping the bomb was completely unnecessary, and secondly because I thought that our country should avoid shocking world opinion by the use of a weapon whose employment was, I thought, no longer mandatory as a measure to save American lives. It was my belief that Japan was, at that very moment, seeking some way to surrender with a minimum loss of 'face'. The Secretary was deeply perturbed by my attitude..."

Dwight Eisenhower, Mandate For Change, pg. 380

Regardless of whether the Japanese government was seriously considering surrender, the bombing forced the decision and was less costly to the Americans (obviously) than a protracted war. Whether a protracted war would have spared Japanese lives as opposed to several more months of brutal warfare is an open question.

It is my opinion that this motivation was one of several competing reasons as to why the Americans decided to detonate nuclear bombs on Japanese civilian centers. In a large part I feel this was simply the natural evolution of the doctrine of total war applied to aerial bombings of civilian targets, first seen in action during the German bombing of Guernica and continued by the Americans both in the fire bombings of Dresden and Tokyo.

Beyond this there was also the ability to justifiably test an atomic bomb in warfare conditions. American military scientists were very interested in seeing the effects of nuclear weapons in many environments (even detonating them underwater to see what would happen). Obviously the most important environment to test it on would be that of urban or military targets. The prior would be unthinkable, outside of a war anyway.

Also, by deploying the bomb America was able to send a strong message about the balance of power after the war. Given that there is always some degree of uncertainty about political relations and military stability after the war, the bomb was certainly a strong message that Americans were not to be messed with. I don't think any of these motivations were alone sufficient in explaining why the American high command decided to drop the bombs; its far more likely that it was a combination of several of these and possibly additional concerns as well.

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The estimated casualty figures for an invasion of Japan were in the millions, lowest I've heard were about a million Americans and 2-3 million Japanese (both killed and wounded). Estimated casualty figures for nuclear bombs (based on known figures for casualties from firebombing cities I believe) were in the order of several tens of thousands per city bombed (the long term effects of radiation sickness were largely unknown and turned out to be less severe than often stated after the war, for decades every death in Hiroshima and Nagasaki due to birth defects and cancer was blamed on the bombs). –  jwenting Feb 1 '13 at 14:06
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tell that to Nimitz and McArthur (and Truman, Marshall, and the rest). Operation Olympic was scheduled for spring 1946 if I'm not mistaken, had the A-bombs and firebombing by B-29s failed to bring about surrender by then. –  jwenting Feb 1 '13 at 20:26
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I think something that is overlooked that we see in spades today's conflicts is that of an active insurgency. Japan, even if it wasn't in a position to effectively fend off an invasion of the island by Allied Forces still had enough spite left in it's military and ruling classes to effectively start and conduct a successful insurgency. Dropping the bomb twice crushed that hope, giving an absolute answer to any idea smacking of resistance. The hidden message could always be touted that if fighting an insurgency was becoming too costly, the Allies could simply leave and nuke the island. –  danstermeister Feb 5 '13 at 18:35
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@mgb-"you can keep doing this for as many years as you wish with no losses." Many years-exactly-and with very dubious results. Military conquest is achieved with boots on the ground. Siege is never more than a preparation for invasion and conquest, and lengthy sieges often end up unsuccessful and are always expensive and difficult to maintain - particulalry at a distance of 5 or 6K miles from the homeland. And besides the military dubiousness of such a siege, USA was tired of war and wanted VICTORY. Politically, a long and expensive siege such as you propose would have been unsustainable. –  Vector Jul 25 '13 at 7:13
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@BrotherJack: Not only the "official reason", but the real reason. As to it's necessity, even after two nuclear bombs had been dropped, the Japanese military leadership remained split on the issue of surrender, half preferring to fight on until everyone was dead. Of course the US could not know that before they dropped the bombs, but it shows that their assessment of the Japanese mindset was correct. They would not have surrendered except after a very long and bloody war. –  Lennart Regebro Aug 4 '13 at 14:08
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The Soviet point of view was that the US used the bomb to threat the USSR.

According the Great Soviet Encyclopedy, article "Nuclear weapons" ("Ядерное оружие") "Применение ЯО не вызывалось военной необходимостью. Правящие круги США преследовали политические цели — продемонстрировать свою силу для устрашения свободолюбивых народов, запугать Советский Союз." "Use of the nuclear weapons was not justified by military necessity: the ruling class of the USA pursued political aims - to demonstrate their strength to the freedom-loving peoples, to threaten the USSR."

But my opinion is that the bomb was actually developed against Germany and only the fact that they surrendered so quickly saved them and brought such misfortune to Japan. The US already spent much money on the new weapon and just could not leave it unused.

It was also instrumental to demonstrate technical superiority over enemy (including Germany, which at the time was considered the most technologically advanced nation), so that to break an image of "advanced" and "civilized" Germans defeated by barbaric and underdeveloped inferior nations (the Germans did not consider the Anglo-Saxons sub-human, but still always empathized that the Germans are the most productive and creative). It was known that Germany developed a range of "wonder-weapons" so that their enemies had to get something to counter-balance such image.

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Germany spent/wasted more money on the V2 project than the US did on the Manhatten Project. –  davidjwest May 2 '12 at 22:41
    
An interesting perspective - if you can provide a link to an online article or a book discussing the Russian point of view, I'll +1 it. –  RI Swamp Yankee Jan 10 '13 at 13:14
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+1 But, it not only saved American lives, but also Japanese lives. –  Dan the Man Feb 1 '13 at 16:47
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@Anixx that's a piece of fine Soviet propaganda, doesn't say anything about the actuality of the situation as it existed at the time. –  jwenting Feb 5 '13 at 7:08
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-1 The US already spent much money on the new weapon and just could not leave it unused. Pejorative, subjective, unsubstantiated, and flies directly in the face of the known history of WW2: The USA intended to invade Japan if they refused to surrender. Truman was intent on achieving total victory against Japan. So it was either the Bomb or a million or two American/Japanese lives lost in a costly and bloody invasion. The US's use of the bomb certainly had an intimidating effect on the Soviets, but to contend that was the reason for its use is ludicrous IMO, regardless of any Soviet claims. –  Vector Jul 24 '13 at 7:08
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The war in Europe had brought the powerful red army, which was mostly responsible for beating Nazis to Berlin in Germany. Us and the soviet Union were having some disagreements on arragements on Europe. Us wanted to let the russians know who is the boss (in the words of Truman) and thus US army roasted nearly half a million Japanese and hurt millions in the coming generations to achieve that. President Truman was instrumental in this by failing to stop the hawks in the army. FDR (Rosevelt would never allow the vision of post war power grab to extend to nuking Japan.) Japanese cities were already incinerated and the most worrisome thing for the Japanese was a Russian Invasion and not the nuclear attack. Also they could not stomach the hanging of their emperor. US delayed assurances to safeguard the emperor until it had exploded the second bomb, on the same day USSR attacked Manchuria, then controled by Japanese forces. Japanese were considered to be sub human at that time and thus the political cost for US politicians was negligable. To understand this well watch Oliver Stone's documentary "Untold history of the USA" episode 2 and 3.

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Downvote. Poorly source, highly speculative, etc. –  Felix Goldberg Jan 11 '13 at 12:41
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not to mention factually incorrect –  jwenting Feb 5 '13 at 7:05
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The Japanese had 4 terms they were demanding in order to "surrender":

  • The emperor would remain inviolate.

  • Japan's borders would be restored to those of summer of 1942, requiring the allies to return to Japanese control every island and country that they had been thrown off of, such as Guadalcanal, Iwo Jima, and the Philippines.

  • Japanese troops would surrender only to Japanese officers. No allied officer or soldier would be allowed to be involved. In effect, the Japanese troops would return to barracks.

  • The Japanese would pay no reparations to anyone for what they did.

To Westerners, this means that the Japanese would be "returning to barracks" and not surrendering in any way that word was understood to mean. The Allies stated clearly "unconditional surrender"

The Japanese felt that they could disgust and demoralize the Allies with the kamekaze attacks and drive the Allies to the bargaining table.

As for the 2nd atomic bomb, we knew what the Japanese were thinking because we were reading their codes. The high command claimed that since it took 4 years for the Allies to make the first atomic bomb, then it would take 4 more years for the second atomic bomb. They knew what an atomic bomb was, and the effects of such weapons, because they had 2 separate atom bomb projects themselves (one in Tokyo using chemical separation of Uranium isotopes, and a diffusion plant in what is now North Korea). Rhodes wrote 2 books (The Making of the Atomic Bomb and Dark Sun) that discussed this along with other national nuclear projects).

A conventinal land invasion of the "home islands" of Japan was expected to cost between 500,000 and 1,500,000 Allied troops. Based on how fierce the Okinawa fighting was, and that it took about 25 Japanese casualties to inflict 1 Allied casualty, it would be expected that a conventional land invasion of Kyushu and Honshu would end up having to kill tens of millions of Japanese civilians before they would really surrender.

Cook, in Japan at War, lists the number of soldiers in Japan at the time of surrender ate 4,335,500, with 3,527,000 stationed outside Japan (mostly in China and Korea).

In the end, the allies did not accept any of the conditions, but promised that the status of the emperor would be determined by the Japanese people.

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Interesting answer. Thank you. –  coleopterist Feb 8 '13 at 7:07
    
The Japanese actually dropped that as a condition and only asked for guarantees about this. The allies responded that the future of the emperor would be determined by the Japanese people. –  Lennart Regebro Aug 15 '13 at 5:32
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Although this question has been well answered, I cannot help but remark that its basis seems quite shaky, and perhaps somewhat pejorative: Seeking to portray the USA as a "bully" in its use of the Bomb.

Even if we grant "they were already on the winning side" (a point that the questioner has failed to document), this was not a valid reason to decline from using the Bomb. The fact remains that on August 5, 1945, the USA had not yet won the war, but was still heavily engaged in the Pacific theatre.

When would the USA actually achieve the victory that they were 'already' heading towards, were they to opt for a victory using only conventional methods of warfare? Would it be six months? A year? This was not clearly known. What would the cost of such a victory be? How many millions of dollars? How many hundreds of thousands of lives, both American and Japanese, would it take? Again: Not at all clear.

[ As an aside I might add that warfare is never entirely predictable. Even the best generals and the most sophisticated technology do not assure victory: Both History (the American Revolution for example) and the world of 2013 (Afghanistan for one) clearly confirm that. Victory in war is never assured until it is achieved. ]

Regardless of the answers to these questions concerning a conventional victory, one thing seemed quite certain: Using the A Bomb would greatly expedite an American victory and minimize its cost, both in blood and in treasure - as indeed History confirms.

So, "they were already on the winning side" was by no means a valid reason for declining to use the Bomb. "Already on the winning side", i.e. the question of an American victory, was not issue. The issue was the cost of such victory, and using the Bomb was clearly the USA's best option in terms of that "cost/benefit analysis".

By way of analogy: Two individual are engaged in hand to hand combat, to the death. They are pummeling one another with severely damaging blows. One of the combatants also has a pistol available to finish the fight quickly, could he only endure his opponent's batterings and get his hands on that pistol.

Now: Even if the armed fighter know he would be able to prevail and pummel his opponent to death, would he not seek to use the pistol rather than endure the many blows and potential injuries that hand to hand combat would require him to endure? In the same way, the USA used the Bomb against Japan.

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... on a Weakened Japan

Compare to German, Japan have controlled 1/6 part of world on august 1945.

Japanese are kamikaze.

https://en.wikipedia.org/wiki/Nagasaki

During the Meiji period, Nagasaki became a center of heavy industry. Its main industry was ship-building, with the dockyards under control of Mitsubishi Heavy Industries becoming one of the prime contractors for the Imperial Japanese Navy, and with Nagasaki harbor used as an anchorage under the control of nearby Sasebo Naval District. These connections with the military made Nagasaki a major target for bombing by the Allies in World War II.

https://en.wikipedia.org/wiki/Hiroshima

During World War II, the 2nd General Army and Chugoku Regional Army were headquartered in Hiroshima, and the Army Marine Headquarters was located at Ujina port. The city also had large depots of military supplies, and was a key center for shipping.

Hiroshima was a main military port and main headquarters.

Nagasaki was a city-military-factory, Mitsubishi produced motors of aircrafts.

It was like nuking The Pentagon and Lockheed Martin's main factories.

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In large part, Hiroshima and Nagasaki were chosen because most of the bigger cities had already been firebombed. –  Andrew Grimm Jul 25 '13 at 13:17
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Also, Nagasaki was only the secondary target for the Fat Man raid - the primary target was Kokura. –  Kobunite Jul 25 '13 at 14:52
    
2Andrew Grimm, partially Hiroshima was bombed by ordinary bomb. 2Kobunite, Kokura was a research's center, it was like DARPA. –  reticulatus Jul 25 '13 at 15:34
    
@reticulatus doesn't matter. Fact is your explanation of why these targets were chosen is largely off the mark. They were simply the next cities on the target list, period. That list included every city in Japan, as there were military and industrial targets in all of them. –  jwenting Jul 26 '13 at 5:18
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The rule of war: Assault takes 3 x lives of attackers against 1 life of defenders. Take a approximate number of Japanese soldiers, multiply to three, this number of USA soldiers went back home in the zinc coffin in the scenario, where the USA continue assault of islands and do not touch Japanese Pentagon(Hiroshima). I say again, "Japanese are kamikaze". –  reticulatus Aug 3 '13 at 15:53
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There's a lot to explain.

Why was the bomb built?

This is too big to answer here! Read the great book The making of the atomic bomb. I'll quote it to answer the other questions.

Why the Allied policy of unconditional surrender?

When the Allied leaders met in 1943 at the Casablanca conference, the phrase 'unconditional surrender' was deliberately left out of the joint statement. But Roosevelt later used it in a hasty speech. and Churchill went along unquestioningly, rather than show any tension between the Allies.

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In January 1943, Franklin Roosevelt met with Winston Churchill at Casablanca. In the course of the meeting the two leaders discussed what terms of surrender they would eventually insist upon; the word "unconditional" was discussed but not included in the official joint statement to be read at the final press conference. Then, on January 24, to Churchill's surprise, Roosevelt inserted the word ad lib: "Peace can come to the world," the President read out to the assembled journalists and newsreel cameras, "only by the total elimination of German and Japanese war power.... The elimination of German, Japanese and Italian war power means the uncon- ditional surrender of Germany, Italy, and Japan." Roosevelt later told Harry Hopkins that the surprising and fateful insertion was a consequence of the confusion attending his effort to convince French General Henri Girard to sit down with Free French leader Charles de Gaulle:

We had so much trouble getting those two French generals together that I thought to myself that this was as difficult as arranging the meeting of Grant and Lee-and then suddenly the Press Conference was on, and Winston and I had had no time to prepare for it, and the thought popped into my mind that they had called Grant "Old Unconditional Surrender," and the next thing I knew I had said it.

Churchill immediately concurred- "Any divergence between us, even by omission, would on such an occasion and at such a time have been damag- ing or even dangerous to our war effort" -and unconditional surrender became official Allied policy.

Why did the Japanese refuse the Allied terms of surrender?

Why not invade Japan?

Why not ask Russia to help invade Japan?

Why drop atom bombs rather than more fire bombs?

Why not warn Japan about the bomb before dropping it?

Why not demonstrate the bomb on an unpopulated area?

Why was the bomb secret?

Why risk a nuclear arms race when the world sees the bomb?

To Szilard's argument that using the atomic bomb, even testing the atomic bomb, would be unwise because it would disclose that the weapon existed, Byrnes took a turn at teaching the physicist a lesson in domestic politics:

He said we had spent two billion dollars on developing the bomb, and Con- gress would want to know what we had got for the money spent. He said, "How would you get Congress to appropriate money for atomic energy re- search if you do not show results for the money which has been spent al- ready?"

Why not keep the bomb secret from Russia?

Byrnes' most dangerous misunderstanding from Szilard's point of view was his reading of the Soviet Union: >

Byrnes thought that the war would be over in about six months.... He was concerned about Russia's postwar behavior. Russian troops had moved into Hungary and Rumania, and Byrnes thought it would be very difficult to per- suade Russia to withdraw her troops from these countries, that Russia might be more manageable if impressed by American military might, and that a demonstration of the bomb might impress Russia. I shared Byrnes' concern about Russia's throwing around her weight in the postwar period, but I was completely flabbergasted by the assumption that rattling the bomb might make Russia more manageable.

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You have explained many things... but I don't think you've clearly answered the question. The question did not ask for an exposition regarding the A-bomb's history, it asked about a very specific point regarding the USA's war strategy in using it, one which is not focused upon in this answer. Perhaps some editing is required? –  Vector Sep 17 '13 at 19:29
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