The December 1938 discovery of nuclear fission by Otto Hahn and Fritz Strassmann—and its explanation and naming by Lise Meitner and Otto Frisch—raised the possibility that an extremely powerful atomic bomb could be created. During the Second World War, Frisch and Rudolf Peierls at the University of Birmingham calculated the critical mass of a metallic sphere of pure uranium-235, and found that as little as might explode with the power of thousands of tons of dynamite. In response, the British government initiated an atomic bomb project, codenamed Tube Alloys. The August 1943 Quebec Agreement merged Tube Alloys with the American Manhattan Project. As overall head of the British contribution to the Manhattan Project, James Chadwick forged a close and successful partnership with the Americans, and ensured that British participation was complete and wholehearted.