of the commission in charge of the RDS-1 testing. Five RDS-1 weapons were completed as a pilot series by March 1950 with a serial production of the weapon that began in December 1951. Detection by the West Some United States Air Force WB-29 weather reconnaissance aircraft were fitted with special filters to collect atmospheric radioactive debris. On 3 September 1949, the Air Force Office of Atomic Energy had a WB-29 fly from Misawa Air Base in Japan to Eielson Air Force Base in Alaska. The plane collected some debris during this flight. This data was then cross-checked with data from later flights, and it was determined that the Soviet Union had effectively tested a nuclear weapon. Response in the West The test surprised the Western powers. American intelligence had estimated that the Soviets would not produce an atomic weapon until 1953, while the British did not expect it until 1954. When the nuclear fission products from the test were detected by the U.S. Air Force, the United States began to follow the trail of the nuclear fallout debris. President Harry S. Truman notified the world of the situation on 23 September 1949: "We have evidence that within recent weeks an atomic explosion occurred in the U.S.S.R." Truman's statement likely in turn surprised the Soviets, who had hoped to keep the test a secret to avoid encouraging the Americans to increase their atomic programs, and did not know that the United States had built a test-detection system using the WB-29 Superfortress. The announcement was a turning point in the Cold War, that had just begun. Once the Soviet Union was confirmed to be in possession of the atomic bomb, pressure mounted to develop the first hydrogen bomb. See also RDS-2 RDS-3 RDS-4 RDS-6s RDS-37 AN602 (Tsar Bomba) Plan Totality Julius and Ethel Rosenberg References External links Video of the Joe-1 Nuclear Test Joseph Stalin 1949 in the Soviet Union 1949 in military history Explosions in 1949 August 1949 events Nuclear proliferation Soviet nuclear weapons testing 1949 in international relations Nuclear weapons policy Nuclear bombs of the Soviet Union Cold War military history of the Soviet Union August 1949 events in Asia