Date

Sep 21, 1949

Description

President Truman had been doubtful that the Soviets had tested the bomb, but on 21 September 1949, he, his aide Steven Early, and Secretary of Defense Louis Johnson saw this memorandum and the supporting documents. Air Force Chief of Staff Vandenberg had written that that "I believe an atomic bomb has been detonated over the Asiatic land mass during the period 26 August 1949 to 29 August 1949. Drawing on the findings of Tracerlab, the AFOAT-1 report concluded that an atomic bomb had been detonated, that the “fission products resulted … from the fission of plutonium” and that the “observed phenomena are all consistent with the view that the origin of the fission products was the explosion of an atomic bomb whose nuclear composition was similar to the Alamogordo bomb.,” with the test occurring between 27 and 30 August.

Vandenberg noted that "[c]onclusions by our scientists based on physical and radiochemical analyses of collected data have been confirmed by scientists of the AEC, United Kingdom and Office of Naval Research" [See documents that follow], In one of the attached memoranda, top scientific and military experts on nuclear weapons, including J. Robert Oppenheimer and Vannevar Bush, endorsed AFOAT/1’s findings.[16] Presumably, this dispelled Truman’s doubts.

The excisions on PDF pages 3 and 5 may be references to the role of the Air Weather Service in providing the aircraft used for the collection of fallout samples.

Source

Declassified Documents Reference System

Document published in following posting(s):

Detection of the First Soviet Nuclear Test, September 1949

Sep 9, 2019