US Air Force to the Secretary of Defense on Long-Range Detection of Atomic Explosions


September 21, 1949

1. I believe that an atomic bomb was detonated over the Asiatic land mass from August 26th, 1949, to August 29th, 1949. I base this on positive information obtained from the system established by the U.S. Air Force for the long-range detection of foreign atomic energy activities.

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

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 agree unanimously with our conclusions.

5. The Joint Chiefs of Staff have been told about the contents of this letter and the report I’ve attached.