It was thought at the time that a fission weapon would be quite simple to develop and that perhaps work on a hydrogen bomb (thermonuclear weapon) would be possible to complete before the end of the Second World War. However, in reality the problem of a regular atomic bomb was large enough to preoccupy the scientists for the next few years, much less the more speculative "Super" bomb. Only Teller continued working on the project—against the will of project leaders Oppenheimer and Hans Bethe.