There was a very young man in my division, Richard Feynman. And I very soon noticed that his ability was far beyond the very great ability of all the rest of my division. And so we collaborated from the beginning. We... we extended Serber's formula for the yield of a nuclear weapon, and there is the Bethe-Feynman formula, which I think is still secret and has worked very well. It has generalized Serber's work to the case when a large fraction of the fissionable material is actually efficient. So very soon I made Feynman another group leader, and we became good friends and remained so after the war. I had the impression at Los Alamos that I was really constantly urged to work harder. We worked eight hours a day, six days a week, and still there was far more to do than we ever could do. Feynman, by the way, turned out to be a wizard, not only in... in theoretical physics, but at one time we got IBM machines, that is mechanical, electrical, calculating machines, and he and another member of my division managed to... to build the whole machine - that is really not one but half a dozen machines - from the tool kit and the instructions that were given together with these tools. After about 10 days, we got an expert, an IBM machinist who was inducted into the Army and was assigned to us. And he just admired it and said he had never seen it before, that people, without previous instruction could put together these machines, they worked. Feynman became the leader of that group. And they calculated all the things that we needed to calculate.
