How did the US comeabout choosing Nagasaki and Hiroshima to bomb?

Cardinal Richelieu

Was there specific reasons behind selecting those two cities over many other potential targets?

Victor

A few factors - they were militarily useful and were largely intact. Quite a few other cities had suffered at least some bombing and presented poorer targets.

On the day, there was a list of alternate targets, depending on things like weather. On the 9 August, Kokura was the primary target and Nagasaki the secondary target.

Read here: http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki#Hiroshima and here: http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki#Nagasaki

meathstevie

Victor wrote: »

A few factors - they were militarily useful and were largely intact. Quite a few other cities had suffered at least some bombing and presented poorer targets.

On the day, there was a list of alternate targets, depending on things like weather. On the 9 August, Kokura was the primary target and Nagasaki the secondary target.

Read here: http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki#Hiroshima and here: http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki#Nagasaki

Pretty much what Victor said, the US knew they had their hands on a serious game changer but could never know the exact effects of an atomic weapon unless it was used in a pretty much intact area.

If for example a similar atomic weapon would have been dropped on Dresden after the RAF's massive incendary attack it would have, radiation excluded, made little or no difference in immedeate physical damage.

claypigeon777

In a conventional attack it thousands of planes flying multiple sorties and dropping thousands of tons of bombs to level one Japanese city to the ground.

Only a relatively intact city would suffice to demonstrate to the Japanese what one plane with one atomic bomb could do.

DazMarz

Also, the underlying theory that the true motivation behind the Atomic Bombings was not just to end the war with Japan quicker, but to flex muscles and show the Soviet Union what the United States had lying in wait...

Victor

DazMarz wrote: »

Also, the underlying theory that the true motivation behind the Atomic Bombings was not just to end the war with Japan quicker, but to flex muscles and show the Soviet Union what the United States had lying in wait...

I'm not so sure. I think if was Fermi who pointed out that it would also let the Soviet Union know that nuclear weapons were possible.

Poland, the British Empire, the French Empire and the USA together took more than a decade to build their first nuclear weapon. The USSR took only 4 years.

tac foley

Both cities were in 'favourable' locations with regard to the local topography - surrounded by low hills that would serve to contain the expected blast.

tac

tac foley

Victor wrote: »

I'm not so sure. I think if was Fermi who pointed out that it would also let the Soviet Union know that nuclear weapons were possible.

Poland, the British Empire, the French Empire and the USA together took more than a decade to build their first nuclear weapon. The USSR took only 4 years.

Whooooooaaaaaaa! You sure have some scrambled information there, Sir! Ten years to build the first nuclear weapon? Poland? French Empire?

Explain, please, how and when Poland built any kind of nuclear weapon? And the French 'empire' disappeared in the late-1800's, too, along with Napoleon III.

The USSR was not a pioneer in nuclear weaponry, but based its knowledge on information obtained by spying, usually Americans - read about Klaus Fuchs and others. The spy scandal court cases filled the news in the fifties. Anyhow, it is easy to be second - the imitator -and quicker, than it is to be the innovator.

tac

knucklehead6

tac foley wrote: »

Whooooooaaaaaaa! You sure have some scrambled information there, Sir! Ten years to build the first nuclear weapon? Poland? French Empire?

Explain, please, how and when Poland built any kind of nuclear weapon? And the French 'empire' disappeared in the late-1800's, too, along with Napoleon III.

The USSR was not a pioneer in nuclear weaponry, but based its knowledge on information obtained by spying, usually Americans - read about Klaus Fuchs and others. The spy scandal court cases filled the news in the fifties. Anyhow, it is easy to be second - the imitator -and quicker, than it is to be the innovator.

tac

I think Victor is saying that it took a Combination of Polish, British, French and American scientists over 10 years to build the first bomb, not that Poland built one, France built one, etc etc....


And france still had a lot of colonies at the outbreak of WW2

tac foley

Précis of the Manhattan Project - the building of America's first atomic bombs.

December 28, 1942
Roosevelt approves detailed plans for building production facilities and producing atomic weapons.
January 13-14, 1943
Plans for the Y-12 electromagnetic plant are discussed. Groves insists that Y-12's first racetrack be finished by July 1.
January 14-24,1943
At the Casablanca Conference, Roosevelt and British Prime Minister Churchill agree upon unconditional surrender for the h powers.
January 16, 1943
Groves selects Hanford, Washington as the site for the plutonium production facilities. Eventually three reactors, called B, D, and F, are built at Hanford.
January 1943
Bush encourages Philip Abelson's research on the thermal diffusion process.
February 18, 1943
Construction of Y-12 begins at Oak Ridge.
February 1943
Groundbreaking for the X-10 plutonium pilot plant takes place at Oak Ridge.
March 1943
Researchers begin arriving at Los Alamos.
April 1943
Bomb design work begins at Los Alamos.
June 1943
Site preparation for the K-25 gaseous diffusion plant commences at Oak Ridge.
Summer 1943
The Manhattan Engineer District moves its headquarters to Oak Ridge.
July 1943
Oppenheimer reports that three times as much fissionable material maybe necessary than thought nine months earlier.
August 27, 1943
Groundbreaking for the 100-B plutonium production pile at Hanford takes place.
September 8, 1943
Italy surrenders to Allied forces.
September 9, 1943
Groves decides to double the size of Y-12.
September 27, 1943
Construction begins on K-25 at Oak Ridge.
November 4, 1943
The X-10 pile goes critical and produces plutonium by the end of the month.
Late 1943
John von Neumann visits Los Alamos to aid implosion research.
December 15, 1943
The first Alpha racetrack is shut down due to maintenance problems.
January 1944
The second Alpha racetrack is started and demonstrates maintenance problems similar to those that disabled the first.
January 1944
Construction begins on Abelson's thermal diffusion plant at the Philadelphia Naval Yard.
February 1944
Y-12 sends 200 grams of uranium-235 to Los Alamos.
March 1944
The Beta building at Y-12 is completed.
March 1944
Bomb models are tested at Los Alamos.
April 1944
Oppenheimer informs Groves about Abelson's thermal diffusion research in Philadelphia.
June 6,1944
Allied forces launch the Normandy invasion.
June 21,1944
Groves orders the construction of the S-50 thermal diffusion plant at Oak Ridge.
July 4, 1944
The decision is made to work on a calutron with a 30-beam source for use in Y-12.
July 17, 1944
The plutonium gun bomb (code named Thin Man) is abandoned.
July 1944
A major reorganization to maximize implosion research occurs at Los Alamos.
July 1944
Scientists at the Metallurgical Laboratory issue the "Prospectus on Nucleonics," concerning the international control of atomic energy.
August 7, 1944
Bush briefs General George C. Marshall, informing him that small implosion bombs might be ready by mid-1945 and that a uranium bomb will almost certainly be ready by August 1, 1945.
September 1944
Colonel Paul Tibbets' 393rd Bombardment Squadron begins test drops with dummy bombs called Pumpkins.
September 13, 1944
The first slug is placed in pile 100-B at Hanford.
September 1944
Roosevelt and Churchill meet in Hyde Park and sign an "aide memoire" pledging to continue bilateral research on atomic technology.
Summer 1944-Spring 1945
The Manhattan Project's chances for success advance from doubtful to probable as Oak Ridge and Hanford produce increasing amounts of fissionable material, and Los Alamos makes progress in chemistry, metallurgy, and weapon design.
September 27, 1944
The 1OO-B reactor goes critical and begins operation.
September 30, 1944
Bush and Conant advocate international agreements on atomic research to prevent an arms race.
December 1944
The chemical separation plants (Queen Marys) are finished at Hanford.
February 2, 1945
Los Alamos receives its first plutonium.
February 4-11, 1945
Roosevelt, Churchill, and Soviet Premier Joseph Stalin meet at Yalta.
March 1945
S-50 begins operation at Oak Ridge.
March 1945
Tokyo is firebombed, resulting in 100,000 casualties.
March 12,1945
K-25 begins production at Oak Ridge.
April 12, 1945
President Roosevelt dies.
April 25,1945
Stimson and Groves brief President Truman on the Manhattan Project.
May 1945
Stalin tells Harry Hopkins that he is willing to meet with Truman and proposes Berlin as the location.
May 7, 1945
The German armed forces in Europe surrender to the Allies.
May 23, 3945
Tokyo is firebombed again, this time resulting in 83,000 deaths.
May 31 - June 1, 1945
The Interim Committee meets to make recommendations on wartime use of atomic weapons, international regulation of atomic information, and legislation regarding domestic control of the atomic enterprise (the Committee's draft legislation becomes the basis for the May- Johnson bill).
June 6, 1945
Stimson informs President Truman that the Interim Committee recommends keeping the atomic bomb a secret and using it as soon as possible without Warning.
June 1945
Scientists at the Metallurgical Laboratory issue the Franck Report, advocating international control of atomic research and proposing a demonstration of the atomic bomb prior to its combat use.
June 14,1945
Groves submits the target selection group's recommendation to Marshall.
June 21,1945
The Interim Committee, Supporting its Scientific Panel, rejects the Franck Report recommendation that the bomb be demonstrated prior to combat.
July 2-3, 1945
Stimson briefs Truman on the Interim Committee's deliberations and outlines the peace terms for Japan.
July 16, 1945
Los Alamos scientists successfully test a plutonium implosion bomb in the Trinity shot at Alamogordo, New Mexico.
July 17 - August 2, 1945
Truman, Churchill, and Stalin meet in Potsdam.
July 21, 1945
Groves sends Stimson a report on the Trinity test.
July 24,1945
Stimson again briefs Truman on the Manhattan Project and peace terms for Japan. In an evening session, Truman informs Stalin that the United States has tested a powerful new weapon.
July 25, 1945
The 509th Composite Group is ordered to attack Japan with an atomic bomb "after about" August 3.
July 26, 1945
Truman, Chinese President Chiang Kai-Shek, and new British Prime Minister Clement Atlee issue the Potsdam Proclamation, calling for Japan to surrender unconditionally.
July 29, 1945
The Japanese reject the Potsdam Proclamation.
August 6, 1945
The gun model uranium bomb, called Little Boy, is dropped on Hiroshima. Truman announces the raid to the American public.
August 8, 1945
Russia declares war on Japan and invades Manchuria.
August 9, 1945
The implosion model plutonium bomb, called Fat Man, is dropped on Nagasaki.
August 12, 1945
The Smyth Report, containing unclassified technical information on the bomb project, is released.
August 14, 1945
Japan surrenders.

tac

Victor

tac foley wrote: »

December 28, 1942
Roosevelt approves detailed plans for building production facilities and producing atomic weapons.

While that might have been the definitive date for a decision to proceed, a lot of the research work had been done before that, work the Soviets wouldn't have had access to.

Jawgap

There's a lot of research to suggest that a major factor in the Americans' thinking was the apparently imminent conflict with the Soviets, as well as the immediate problem of forcing the Japanese to recognise they were beaten.

Truman wanted the Soviets to know that not only did the US possess the bomb but they were willing to use it. He told Stalin they had a working device at Potsdam and stalled on making anything beyond minimal agreements with the Soviets until Japan had been bombed. There's also plenty of evidence showing how Truman orchestrated a delay in holding the Potsdam conference until the Alamogordo / Trinity test detonation had been successfully completed.

General Groves said in an interview that in his view "Russia was our enemy, and the Project was conducted on that basis” - the 'larger' purpose of the Project was to assert primacy over the USSR, especially in Europe.

On the more direct question as to why those cities were chosen, you can access the Target Committee Minutes online......

Section II of this webpage - The Atomic Bomb and the End of World War II, from the US National Security Archive.