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 instead of tonnes, as everyone had assumed, as little as would suffice, which would explode with the power of thousands of tonnes of dynamite. In response, Britain initiated an atomic bomb project, codenamed Tube Alloys.