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Did the US Consider NOT Using the Atomic Bombs? & The Operation Sea Lion Fantasy | WW2 Brain Bucket

WW2 historian Paul K. DiCostanzo explores if the US ever considered not using the Atomic bomb, and why Operation Sea Lion never occurred.



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In this installment of the WW2 Brain Bucket, WW2 historian Paul K. DiCostanzo examines your questions about if the US ever considered not using the atomic bombs, and the feasibility of Operation Sea Lion – Nazi Germany’s plan for invading Britain in autumn 1940.

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“Did the Allies ever consider not dropping the Atomic bombs on Japan? Would they ever not have chosen to do so?” – Wyatt, Texas

To frame the answer to your question, it is important to make clear this is not an evaluation of what primarily triggered Japanese surrender. Was it the atomic bombs? Was it the Soviet invasion of Manchuria? Those issues are not on the table. Nor is it a discussion regarding the morality of having used the atomic bombs. Instead, it is a look at Allied decision making relative to how and why they chose to use the atomic bombs, based on the information available at the time, the strategic situation, and it’s critical political considerations. 

So, would the US have ever chosen to withhold the atomic bombs use against Japan? In the eyes of top American war planners, any scenario short of the Japanese unexpectedly accepting the Potsdam Declaration – the reaffirmation by the Allies in their calling for unconditional Axis surrender – occurring prior to the availability of the atomic bombs, the answer is an unequivocal “no.” When analyzing both the political and military ramifications of the first US atomic bombs becoming available for use in July 1945, there is exactly zero chance the Allies would have passed on using them against Japan if they were still at war.

There are myriad reasons why the United States chose to use the atomic bombs. To understand the Allied war planner’s and President Truman’s decision, one must consider the combination of the resources invested in the bomb’s development, the aspiration for it’s potential as a strategically significant weapon, the political fallout of not using them prior to a conventional invasion of Kyushu and Honshu, and the lack of viable conventional alternatives to force Japanese capitulation. These aforementioned factors made the use of the atomic bombs the most preferable option available to Allied war planners at the time.

Before fully diving into this rabbit hole, let’s discuss why the Western Allies constructed the atomic bombs in the first place. 

Why The Allies Originally Developed the Atomic Bomb

As many know, the atomic bombs were developed in a top secret joint US/British/Canadian venture, the Manhattan Project, to outpace Nazi Germany’s goal for creating the atomic bomb themselves. What the western Allies couldn’t have known at the time – yet is now clear to historians – is that Nazi Germany was nowhere close to successfully building their own bomb.

Germany by 1942 had focused their efforts primarily into other so-called “Wunderwaffe,” or Vengeance Weapons. Wunderwaffe projects notably included the development of the infamous V-1 “Flying Bomb,” it’s successor the V-2 rocket, as well as the jet engine aircraft Me 262 to name a few.

Third Reich research towards developing an atomic bomb experienced numerous complications; including decentralized research efforts, a combination of myriad government inter-departmental and project in-fighting, all of which are common fare in many other endeavors during the Third Reich at war. Germany’s war effort in every facet was experiencing an ongoing competition for scarce material resources, Wunderwaffe projects included.

These matters were further confounded by many major figures in the Reich scheming to have these projects fall within their personal fiefdoms, aiming to receive sole credit for their success. The strictly scientific minds involved in Nazi Germany’s research and development were also revealing in this respect.

Werner Heisenberg was Nazi Germany’s foremost theoretical physicist, a pioneer in quantum mechanics, the creator of the famed Heisenberg Uncertainty Principle, and recipient of the 1932 Nobel Prize in Physics. Heisenberg was also one of the major professional scientific point-men in Nazi Germany’s construction of an atomic bomb, and privy to many of the details relating to Nazi Germany’s progress toward building their first atomic atomic bomb. Heisenberg upon first learning of the atomic bombs use against Japan was in abject disbelief.

Heisenberg could not imagine how the Western Allies constructed it, based on the countless research hurdles faced in his quest to do so. He initially thought the news was either Allied propaganda, or perhaps a uniquely destructive – but conventional – bomb. Heisenberg was quickly disabused.

Heisenberg’s reaction is remarkably telling, as he was among the few in Germany who had the relevant insights to arrive at such an original conclusion. Heisenberg was not alone, as there were higher ranking members of Germany’s government who had expressed similar sentiments about the prospects for its construction years earlier. 

Hitler himself thought weaponization of the atomic bomb wasn’t feasible in time for use in the war. Hitler in holding that belief directed resources be allocated toward more potentially useful Wunderwaffe projects. Such are the ropes in a despotic totalitarian state, where the whims of the all-powerful leader dictate said priorities. Unknowingly to the Allies, it gave them a tremendous advantage in the high stakes of creating the first atomic weapon.

The Allies original intent was to use their atomic bombs on Germany, however Nazi Germany’s unconditional surrender in May 1945 occurred two months prior to the first successful test detonation in New Mexico.

When getting to the heart of the Allies unswerving decision to eventually use the atomic bombs, theirs was more than a mere wartime opportunity that dictated its eventual use. The financial dynamics of the Manhattan Project played a definitive role in its own right. 

Follow the Money: The Cost of Developing the Atomic Bombs

The Manhattan Project was a remarkably high expenditure, costing the US $2B ($28B as of 2020) to complete. The project was the second largest US wartime expenditure after the $3B price tag for the B-29 contract. The Manhattan Project’s cost alone made the atomic bombs usage a near fait-accompli, if the Allies still found themselves at war when they became available.

When considering the governmental realities of undertaking a program as ambitious and expensive as the Manhattan Project, it accompanies a great political pressure to see the final product prove useful towards Allied victory.

Forgoing their use would have lead to later accusations of profligate spending, questions about why that same financial appropriation was not used towards other efforts that could have proven useful in the war, as well as outright questioning the Truman administration’s judgement. Financial appropriations aside, the atomic bombs had additional political sensitivities as well. 

The Political Implications of Not Using the Atomic Bombs – Needlessly Squandering Allied Lives

Powers engaged in total war against an implacable foe do not withhold usage of a weapon that might be a quantum leap in weapons technology. Especially a weapon that might also have revolutionary strategic implications.

Nor would any wartime leader want to face the uproar of their nation – especially in a Western democracy – answering for why their sons and daughters died during a conventional invasion of Japan, that might have been made otherwise unnecessary with use of the atomic bombs. On a political basis, such a situation is odious at best.

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President Truman gave the final green light  to bomb Hiroshima and Nagasaki, and nor would FDR have hesitated to do the same.

When one takes a prospective view of the war during the summer of 1945, it’s clear Allied war planners had much to consider. Especially the numerous particulars of deploying the atomic bombs. 

The Secret Debate of How, When & Where to Use the Atomic Bombs

The US “Interim Committee” founded in May 1945, was a small consultative body focusing on early US nuclear doctrine and use of atomic energy; prior to establishing the policy of full civilian control of nuclear weapons and energy that exists to this day.

Interim Committee members included a select few with the national security clearance allowing them full knowledge of the highly secretive and sensitive Manhattan Project; such as President Truman, Secretary of State James Byrnes, and Secretary of War Henry Stimpson to name but a few. 

The committee’s foremost priority was advising President Truman on how the atomic bombs might best be used against Japan. 

The internal deliberations of the Interim Committee – in so far as is known – never seriously floated the prospect of withholding use of their new weapon.

Before discussing further how the atomic bombs might have been used, Allied war planners foremost needed to address another burning question: Was there any additional feasible conventional strategic alternatives to defeat Japan beyond using the atomic bombs, or an outright invasion of the Japanese home islands?

The Blockade Option: A Lesser-Known and Problematic Alternative to Invasion and Dropping the Atomic Bombs

During the Second World War in the Pacific, the US conducted a highly effective naval blockade of the Japanese home islands – one now all but forgotten in popular historical memory. The Battle of the Atlantic and the German U-Boat campaign interdicting Allied merchant shipping dominates most historic attention. However, the most effective maritime interdiction campaign of the war was enacted by US Navy submariners against the Empire of Japan.

Aside from a conventional invasion of Honshu and Kyushu, marine interdiction of Japan was the only other realistic conventional alternative the Allied powers had for potentially coercing Japanese capitulation, thus ending the war. Yet that approach possessed clear and considerable drawbacks. 

The nature of economic strangulation by naval blockade in the Pacific was a so-called, “Known-Unknown,” requiring an unknown period of time to potentially succeed. For all the wartime resources at the command of Allied forces in the Pacific during the summer of 1945, time was never among them.

Warfare dictates maintaining the initiative over the enemy, thus never providing one’s enemy the benefit of additional time. Hence the cost in possible time to undertake a successful blockade may have proven very high indeed, if it worked at all.

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As is invariably the case in war, decisive action was required to achieve Japanese surrender. The Allies by waiting for a blockade to succeed would provide Japan further time to enact greater defensive measures for resisting a conventional Allied invasion of Honshu and Kyushu – if it became necessary. In doing so, the already tremendous cost of a conventional invasion would have certainly increased as well.

Moreover the so-called “Known-Known,” was that the Japanese conception of resistance did not recognize privation in the least. There was a genuine Allied fear that all Japanese people would continue to resist to the point of their own collective obliteration, and were unlikely to value the dwindling means of their basic sustenance in the process. Indeed by late in the war, Japan was taking active steps to psychologically and physically train their civilian populous to do just that.

With the highly problematic conventional alternatives understood, how else might the Allies have used the atomic bombs other than how they eventually did?

Options for How the US Could Have Used their Atomic Bombs Differently

During the top level discussions on how to use the atomic bombs, the merits of a “technical demonstration” for Japanese benefit were debated. The “technical demonstration” would be an unambiguous detonation at a safe but visible distance; making clear the novel devastating weapon the Allies possessed, ultimately serving to encourage immediate surrender.

The “technical demonstration” concept was dismissed, primarily due to the committee’s belief that only the use of the bomb on a viable Japanese target would properly convey the reality of their new weapon’s lethality as intended. 

The “Target Committee” – the immediate predecessor to the Interim Committee – was headed by General Leslie Groves in early 1945. General Groves was also the primary professional military head of the Manhattan Project.

As the Target Committee’s name indicates, these discussions were considering the best possible locations, as well as best possible uses, for dropping the atomic bombs.

According to the Target Committee, they generated a number of options for the bombs use:

Use as a tactical weapon, assisting the conventional invasion of the Japanese home islands.

Use as a demonstration before primarily Japanese civilian observers, the aforementioned “technical demonstration.”

Use as a demonstration before a Japan military target, with primarily military observers.

Use against a primarily military target.

Use against a city with a military target, providing advance warning.

Use against a city with a military target, forgoing advance warning. 

As indicated above, it’s clear what the final choice was for Allied war planners. The next challenge was deciding where to use the bombs.

List of Target Locations

Aside from the eventual targets of Hiroshima and Nagasaki, the original draft of target candidates cities included Kyoto as the foremost preferred target. Kyoto was rejected for a number of reasons. Some of those reasons included its status as Japan’s long famous historic cultural epicenter, containing Emperor Hirohito’s personal residence.

Kyoto was removed from the list, partially in thanks to Henry Stimpson. It is said that Stimpson held a personal fondness for Kyoto, after honeymooning there with his wife many decades prior. Stimpson sought to protect this cultural treasure, fully understanding that it would create outright resentment by the Japanese for generations if it were obliterated.

Kyoto’s bombing would also have likely killed Emperor Hirohito. Hirohito as Emperor was thought by his subjects to be a living deity – the direct ancestor of the Shinto Sun Goddess Amaterasu. The Allies by using the atomic bomb on Kyoto might have unnecessarily created a divine martyr of Hirohito, reinforcing the already implacable resistance of the Japanese people.

Hirohito was also the lone figure who through his divine status could unilaterally command Japan’s surrender. In total, all of these outcomes were well worth avoiding at all costs by nixing Kyoto from the list.

Tokyo for all its importance was not considered, as shortly before it was almost completely destroyed following the campaign of Allied incendiary bombings. Indeed, choosing mainland targets was very difficult, as so many Japanese cities had been leveled by Allied conventional bombing. 

When it comes to the decision to use the atomic bombs against Japan, it’s important to also consider how Allied war planners viewed their Japanese enemy in July 1945. In addition to how that impression informed their decision making. 

How the Allies Viewed Japanese Resistance in Summer 1945

In late July 1945, the US had just achieved  victory on Iwo Jima and Okinawa at bitterly high cost. These battles were among the most brutal of the war, and clearly indicated that any conventional invasion of the Japanese home islands – designated Operation Downfall – might take millions of Allied and Japanese lives to complete. Nor was there any way to predict how long such a fight would last.

Okinawa and Iwo Jima were savage, close quarter engagements that demonstrated the zeal of Japanese resistance. It made a deep impression on how much the Japanese were prepared to sacrifice, their utter rejection for the concept of surrender, and how that may manifest in defense of their home islands.

During the war itself, the Allies held between 20,000 and 50,000 Japanese prisoners of war. Compared to the estimated 140,000 Allied POWs held in captivity by Japan. Long story short, surrender was a rare occurrence by Japanese forces. By comparison, the UK and Britain each held roughly 400,000 European Axis POW’s during the war. Japan was the unambiguous exception among all belligerents involved in the conflict. 

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Unless otherwise instructed to surrender by Emperor Hirohito, or ranking government officials, Allied leaders had legitimate reason to fear that every Japanese man, woman and child may have fought to their extinction against any such invasion of mainland Japan.

Within the context of the greater war, the Japanese rejection of surrender was remarkably unique, entirely foreign to Western sensibilities, and in fact almost otherworldly in the eyes of the American and British troops locked in combat against them.

During the fighting in the European or North African theaters, surrender was far more commonplace and mostly accepted by all sides – despite the treatment of POW’s varying significantly. Seldom was there such a constitutional elan to avoid being taken prisoner at the cost of one’s own life. Even for the soldiers of the Red Army that sought to avoid surrender at all costs, their attitude was predicated on their expected treatment by the Germans in captivity, and the understandable dread of later repatriation to the USSR should they survive their captivity. Never was it treated as a divine mandate – as it so clearly was for the Japanese. 

Yet while the Allies understood the implacable nature of Japanese resistance, accompanied with their aspirations for the  potential of their new atomic bombs, they were not at all certain about the atomic bombs reliability. Nor was anyone placing bets that the bombs use might bring a swift end to the war despite their greatest hopes.

The Atomic Bomb was no Golden Ticket

A common popular trope that’s become wound up in the history of the atomic bomb’s usage is the ahistorical belief that it would invariably promote immediate Japanese capitulation. Furthermore, it’s often retrospectively assumed that the Allies thought they were near victory in August 45’.

Allied leaders in the summer of 1945 had no clear expectations that the atomic bomb’s use would necessarily force an end to Japan’s fight whatsoever. When peace transpired in August 1945, it genuinely caught the Allies by surprise. 

Nor could Allied war planners have proceeded from such an assumption, as it would have hindered preparation for what they thought was the likely course of action regardless: a conventional invasion of the Japanese home islands.

Furthermore, it’s critical to note that Japan did not outwardly flinch initially following the first atomic bomb’s use on Hiroshima. It was not until the second atomic bomb was dropped on Nagasaki, accompanied by the Soviet invasion of Manchukuo (Manchuria), that Hirohito broke the Imperial War Council’s deadlock over the decision to surrender.

Japanese surrender – when it eventually came forth – was a major shock to the Allies for several reasons. It was unknown how much the atomic bombings might have impacted the thinking of Japanese war planners or Hirohito himself. Or that dropping the atomic bombs might lead to his uncharacteristic unilateral intervention to ending hostilities.

Moreover, there was sound and reasonable doubt that the bombs would function at all. The Allies had only the bomb’s first successful test detonation in July 1945 from which to proceed. One could never reasonably place all their bets on a revolutionary technical advancement, especially after only a single successful test. 

Nor were the Allies altogether ready for peace. The Allies were planning for the war against Japan to last into 1946 or 1947 at the earliest.

Was the Use of the Atomic Bombs Inevitable?

As a rule, nothing in history can be thought inevitable… except for a German counter-attack. Though when one examines the numerous factors that lead to the Allies first developing, and then using atomic bomb; including the financial cost of doing so, it’s various intra-governmental as well as domestic political implications, and its potential strategic magnitude while fighting a global conflict, it’s nigh impossible to imagine the Allies choosing otherwise.

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Suggested Reading:

  • “Hell to Pay: Operation Downfall and the Invasion of Japan, 1945-1947” by D.M. Giangreco
  • “Retribution: The Battle for Japan, 1944-1945” by Max Hastings
  • “Truman” by David McCullough

Suggested Viewing:

  • ”Kamikaze” (1995), BBC Timewatch
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Paul K. DiCostanzo is the Managing Editor for TGNR. He is a noted public speaker, an emerging historian of the Second World War, a vocal advocate for Crohn’s Disease/Ulcerative Colitis, and highly regarded interviewer. Paul K. DiCostanzo is Co-Host for the A.D. History Podcast. The A.D. History Podcast explores world history of the last 2000 years in an unprecedented fashion; with each episode covering a 10 year period beginning in 1AD, until reaching the present day. Ultimately finding the forgotten, as well as overlooked threads of history, and weaving a tapestry of true world history. Paul is author of the reader submitted Q&A column: WW2 Brain Bucket. The Brain Bucket answers readers submitted questions on all things regarding the Second World War. Paul has served as Managing Editor for TGNR since March 2015. Prior to TGNR, Paul has a background in American National Security and American Foreign Policy.