RDS-1

RDS-1 also refers to the model of nuclear gravity bomb put into weapons production, with 29 bombs stockpiled by 1951. The United States initially detected the test's nuclear fallout four days later via its anticipatory program for aerial sampling regions near the Soviet Union. On 23 September, US President Harry S. Truman publicly announced evidence that "an atomic explosion occurred in the U.S.S.R." The Soviet government initially denied the report, suggesting a misidentification of its excavation works for hydroelectric power, however it made cryptic statements before and after the test about its nuclear capability. In response, the United States government ordered a crash program to develop the "Super" i.e. hydrogen bomb, accelerating the nuclear arms race.

There are several explanations for the Soviet code-name of RDS-1, usually an arbitrary designation: a backronym "Special Jet Engine" (Реактивный двигатель специальный, Reaktivnyi Dvigatel Spetsialnyi), or "Stalin's Jet Engine" (Реактивный двигатель Сталина, Reaktivnyi Dvigatel Stalina), or "Russia does it herself" (Россия делает сама, Rossiya Delayet Sama). Later weapons were also designated RDS but with different model numbers. The bomb is also known as Izdeliye 501 (изделие 501 'Device 501').

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.

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. The announcement was a turning point in the Cold War, that had just begun, and marked the beginning of the nuclear arms race. Once the Soviet Union was confirmed to be in possession of the atomic bomb, pressure mounted to develop the first hydrogen bomb. Truman was informed of the possibility of such a weapon thirteen days later, on 6 October 1949.

Following Truman's announcement, Soviet state newspaper TASS released a report. It suggested the West had detected signatures from excavation works in the Soviet Union. Nonetheless, it stated the Soviet Union possessed nuclear weapons, and noted the November 1947 claim by Minister of Foreign Affairs Vyacheslav Molotov, that the Soviet Union understood the "secret" of nuclear weapons design. Deputy Chairman of the Council of Ministers Kliment Voroshilov internationally reiterated nuclear capability five months later in March 1950. The RDS-1 device was put into weapons production from 1949 to 1951, stockpiling 29 bombs, compared to the US' 1947 to 1949 production of 120 first-generation Fat Man bombs.