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Memorandum by the Chief of Staff, US Air Force to the Secretary of Defense on Long Range Detection of Atomic Explosions
21 September 1949

1. I believe that an atomic bomb has been detonated over the Asiatic land mass during the period 26 August 1949 to 29 August 1949. I base this on positive information that has been obtained from the system established by the U.S. Air Force for the long range detection of foreign atomic

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energy activities.

2. Fission products have been collected since 3 September 1949. Although the system is only partially developed, we have been fortunate in securing sufficiently large and fresh samples for effective scientific analysis. The cloud containing fission products was tracked by the U.S. Air force from the Kamchatka peninsula to the vicinity of the British Isles where it was also picked up by the Royal Air Force.

3. Conclusions by our scientists based on physical and radiochemical analyses of collected data have been confirmed by scientists of the AEC, United Kingdom Office of Naval Research. 

4. At my request, Dr. Vannevar Bush, Dr. J. Robert Oppenheimer, Dr. Robert Backer and Admiral William S. Parsons have reviewed our findings and concur unanimously in our conclusions.

5. The Joint Chiefs of Staff have been informed of the contents of this letter and the attached report.