British contribution to the Manhattan Project
Britain initiated the world's first research project to design an atomic bomb in 1941. Building on this work, Britain prompted the United States to recognise how important this type of research was, helped the U.S. to start the Manhattan Project in 1942, and supplied crucial expertise and materials that contributed to the project's successful completion in time to influence the end of the Second World War.
Source: Wikipedia — British contribution to the Manhattan Project (CC BY-SA 4.0)