1949

RDS-1

Soviet Union conducts its first nuclear test, RDS-1

The bomb was assembled during the night and finished only hours before its 7:00 a.m. detonation — and the Americans learned of it from radioactive dust caught by a weather plane five days later.

29 August 1949, 7:00 a.m., Semipalatinsk

At 7:00 a.m. local time on 29 August 1949, the Soviet Union detonated its first atomic bomb at Test Site No. 2, about 170 kilometres west of Semipalatinsk in the Kazakh SSR. The tower-mounted plutonium implosion device, designated RDS-1 — Joe-1 was the American name — produced an estimated yield of 22 kilotons.

The design closely followed the American Fat Man/Gadget implosion configuration, whose details had reached the Soviet program through wartime intelligence. Around the tower, engineers had placed houses, military equipment and experimental structures to measure what the blast would do to them.

A handwritten report to Stalin

Scientific director Igor Kurchatov ran the test; Lavrentiy Beria, chairing Stalin's Special Committee, attended. Their preliminary report to Stalin survives as a handwritten document dated 30 August — the day after the blast.

The weapon itself had been designed principally at the secret KB-11 bureau at Sarov under chief designer Yulii Khariton — not, as often written, 'at the Kurchatov Institute'; Kurchatov's Laboratory No. 2 directed the broader scientific program.

How the secret got out

The United States did not detect the explosion as it happened. A WB-29 weather-reconnaissance aircraft intercepted radioactive debris on 3 September — five days later — and analysis concluded the material came from a plutonium bomb resembling the Trinity device. President Truman announced the evidence publicly on 23 September.

The test ended the United States' exclusive possession of a demonstrated nuclear capability, though it did not instantly create a large deployed Soviet arsenal. Even the name RDS keeps its mystery: expansions like 'Russia Does It Herself' are retrospective jokes, not an established original meaning.

Sources

Researched 23 Aug 2026 6 sources 3 audit passes Date corrected

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date corrected. The research places this at 1949-08-29.

What the sources leave uncertain

RDS has acquired several later expansions—such as 'Stalin's Jet Engine' and 'Russia Does It Herself'—but historians treat these as retrospective jokes or backronyms rather than a securely established original meaning.
The 22-kiloton yield is an estimate commonly used in scholarly histories, not a directly measured exact figure.
Accounts distinguish the tested experimental device, production models and fully assembled operational stockpiles; later claims of exactly 29 ready bombs by 1951 should be treated cautiously.