The United States initiated the Manhattan Project in 1942 in collaboration with the United Kingdom.
Notes on verification
Well-documented historical fact confirmed by multiple independent sources including Wikipedia, Atomic Heritage Foundation, and academic publishers. Minor simplification in that Canada was also a partner and full UK-US integration solidified via the 1943 Quebec Agreement. [tier=silver indep_score=0.875 clusters=2 claim_tier=everyday]
Sources
- History of nuclear weapons (wikipedia)
- https://ahf.nuclearmuseum.org/ahf/history/british-nuclear-program/ (corroboration)
- https://cup.columbia.edu/book/the-manhattan-project/9780231131537/ (corroboration)