Tube Alloys was a codename of the clandestine research and development programme, authorised by the Government of the United Kingdom with participation from Canada, aiming to develop nuclear weapons for the United Kingdom's nuclear weapons programme during the Second World War. Starting before the Manhattan Project (the Western Allies' nuclear bomb project) in 1942, the British efforts were kept highly classified such that they had to be referred to by code even within the highest circles of government. At the end of the Second World War, Tube Alloys came to refer specifically to the element plutonium, whose very existence was secret until its use in the atomic bombing of Nagasaki.