One of the very ingenious people in Los Alamos, Seth Neddermeyer, had idea that instead of starting with two pieces, we should start with a shell and surround it with high explosive and have the whole thing converge and that might work fast enough. It was a proposal that looked good but was not yet accepted. In the meantime, I had a personal proposal. I found in many other instances that when I had a problem it always could be solved by getting the advice of somebody who was, in my opinion, better than anybody else, a fellow Hungarian, Johnny von Neumann. Oppenheimer was under orders to keep Los Alamos closed, or almost closed, not letting- let many people in but when he got convinced that somebody would be really needed, he was very good at getting him so we got permission for Johnny von Neumann to come in and help us. We told the problem, he made some suggestions, I won't reme- I won't mention them, they did not turn out to be very good. But that first evening, I invited Johnny for dinner and that dinner I remember, for reasons more than one. I remember sitting with him near the heating equipment which did not function perfectly and which would send off a loud report of some inst- unstable condition once every half hour. I don't know that Johnny was really alarmed but he told me- I would feel that it is a real shame to be killed in Los Alamos by a mere sub-critical explosion. That was a part of it. Another part was that I told Johnny about the proposal of Seth Neddermeyer and Johnny did something extremely simple, I don't know why all of us did not do it earlier. He assumed, as was the sort of obvious thing to assume, that uranium or plutonium would be incompressible and then let it be sent in by the velocity that an explosive could produce. As the material got into smaller and smaller radii, in order to make room for the incoming material, the shock formed had to go faster and faster. The material had to accelerate. And in order to do so, had to have a big pressure. And Johnny came to the conclusion you could do that; in the process you would produce more than 100 million atmospheres. And I have told you that at the George Washington University we had conferences. One of them was about the interior of the Earth, where I learned that a pressure- at a pressure of barely a few million atmospheres, not 100 million, iron in the center of the Earth would be compressed. If Johnny was right about these big pressures, then the material, plutonium or uranium, would surely be compressed and compressed material can lead to neutron multiplication in smaller amounts. You could get nuclear explosions by the method of an initial implosion, we could get the job done, with less materials, at a much earlier time, possibly before the end of the war. That point we put next morning before Oppenheimer. He caught on very fast. The whole program of the laboratory was changed. The implosion was put down as number one priority.