The United States initiated the Manhattan Project in 1942 in collaboration with the United Kingdom.
Notes on verification
Well-corroborated by multiple independent sources including Wikipedia's main and specialized articles; minor simplification of the multi-stage UK-US collaboration timeline (Tube Alloys, Quebec Agreement) but core facts are accurate.
Sources
- History of nuclear weapons (en.wikipedia.org)
- https://ahf.nuclearmuseum.org/ahf/history/british-nuclear-program/ (ahf.nuclearmuseum.org)
- https://cup.columbia.edu/book/the-manhattan-project/9780231131537/ (cup.columbia.edu)
- https://www.lanl.gov/media/publications/the-vault/1023-los-alamos-and-the-british-mission (lanl.gov)
- https://home.nps.gov/mapr/learn/historyculture/timeline.htm (home.nps.gov)