The United Kingdom began the world's first nuclear weapon…

History1940sUnited Kingdomhigh confidence

The United Kingdom began the world's first nuclear weapons research project, codenamed Tube Alloys, in 1941.

Notes on verification

Confirmed by Wikipedia, a peer-reviewed Nuclear Technology article, and UK Defence Journal, all agreeing on the 1941 start date and the UK's priority in establishing the first nuclear weapons programme. [tier=silver indep_score=0.925 clusters=2 claim_tier=notable]

Sources

History of nuclear weapons (wikipedia)
https://www.tandfonline.com/doi/full/10.1080/00295450.2021.1910004 (corroboration)
https://ukdefencejournal.org.uk/britain-and-nuclear-weapons-the-second-world-war-to-the-21st-century/ (corroboration)

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