Japan’s Atom Bomb Program


Most Americans are unaware that during World War II Japan had two programs seeking to build an atomic bomb.

In 1939 Dr. Yoshio Nishina,  a Japanese nuclear physicist, recognized the potential of the then theoretical atomic bomb.  ( In 1934 Professor  Hikosaka Tadayoshi theorized about such a bomb.)  In 1940 he spoke with Lieutenant-General Takeo Yasuda, director of the Army Aeronautical Department’s Technical Research Institute, about the potential of an atomic bomb.  The Japanese Army began its program to develop an atomic bomb in April 1941.

Meantime, the Japanese Navy began its own program creating the Committee on Research in the Application of Nuclear Physics chaired by Dr. Nishina in 1942.  The Navy’s project ended in 1943 when the Committee reported that while such a bomb was feasible it predicted that it would be difficult for even the United States, with all its resources, to harness the power of the Atom in time to have an impact on the War.

However, the Navy dropping out had no effect on the Army’s program which continued on to the end of the War, hampered both by lack of materials and by ever heavier US bombing.  How far the Japanese got is open to speculation as the project was veiled in the deepest secrecy during the War, and most documents pertaining to it were destroyed by the Japanese prior to the Surrender.

There have been persistent rumors since World War II that the Japanese tested a nuclear device prior to the end of the War, either on an uninhabited island off what is now North Korea, or near Konan in what is now North Korea  on August 12, 1945.  The documentation is currently lacking to substantiate those claims.  What is certain however, is that the Japanese had an ongoing atomic bomb project at the end of the War.  Given enough time, I think it is foolhardy to think that one of the more inventive nations on Earth would not have found their way around road blocks and managed to have constructed an atomic bomb.  The development of the atomic bomb during World War II was indeed a race, and not just against the Germans.





Published in: on August 24, 2015 at 5:30 am  Comments (1)  
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  1. Initially many scientists could and did hope that some principle would emerge which would prove that atomic bombs were inherently impossible. This hope gradually faded.
    Smyth Report 1946

    An extract from the Tonizo Dossier.

    Meeting on Uranium research at the Nishina laboratory. 6th July 1943.
    Attendance: Dr. Nishina, Gen. Nobu-uji, Ishida ( gishi / engineer ?)

    Dr. Nishina; The minimum mass of uranium 235 is about 10Kg and is determined by the balance between the neutrons generated by fission and those lost though the surface. If too many are lost then there will be no sustained chain reaction. Though this critical mass is about 10 Kg, it will not make a bomb, there needs to be extra, assume an extra 10 Kg (1).
    Gen. Nobu-uji asks if this extra will also under go fission. Nishina says, no, only a portion will undergo fission, the rest will be lost in the explosion (2). At present it is not within our capability to implement such a device.
    There are other reasons why a bomb is not practical and therefore not recommended ( fu-tokusaku. In order to achieve the largest possible explosion, the bomb needs to be held ( hoji ) together for 1/30 to 1/20 [micro]* second and to achieve this it requires a large and heavy tamper or reflector (3). The weight would be enormous ( jindai ), therefore as a device is considered impractical and as a bomb not suitable ( tekito narazaru ).
    (1) Modern nuclear parameters yield a critical mass for U235 of about 17 Kg with a substantial reflector. The Hiroshima bomb used 80% U235 and was about 2.8 critical masses.
    (2) Only about 700 grams of U235 out of 64 Kg underwent fission at Hiroshima., the rest being lost in the explosion.
    (3) Due to the exponential increase of the fission process, 99.5% of the energy is released in the last 4.6 fission periods. At about 10 nano-seconds per period this is 46 nano-seconds or approx. 1/25 micro-second. During this period the energy released must overcome the inertia of the tamper holding ( hoji suru ) the device together.
    * The word micro is missing from the text, micro-second = haku man bun no ichi byo.

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