My friend Dave Giggs, the seismologist who helped me to understand the earthquake wave by which I noticed the first nuclear explosion, he pushed the idea and I liked it: perform nuclear experimentation underground. Of- offhand one would imagine that such underground tests would limit the ability to observe detailed effects. It turns out that this limitation is not very serious and a lot can be done by underground experiments. The first shot of that kind was fired before the moratorium, before the Soviets and Americans stopped testing in '58. The eventual result was that when the Russians resumed testing and we resumed testing, shots were fired on both sides in an accelerated fashion, but negotiations also went on toward a permanent elimination of tests. I felt at that time that the demand to stop atmospheric testing was so strong that in fact it was irresistible and also that what we needed to do could be done by testing underground. The great advantage being that to the extent that you are worried about radioactivity, it will be contained, it would not spread at all, and it also turned out that with appropriate instrumentation you could find out practically everything that you wanted to find out about nuclear explosions by such underground tests. There was a last component. It was and is more difficult to eliminate underground testing in such a way that the actual elimination can be checked. Underground explosions do cause, do bring about earthquake waves that can be noticed, but a result of a group of excellent people, of the work of excellent people in southern California, this earthquake wave could become practically innoticeable- unnoticeable if the explosion is not too big and is fired in a cavity of a sufficient size. In the end we wound up with a treaty limiting testing to underground tests and this was in the end done in a realistic manner so that the treaty actually said most of the things that in a practical way could indeed be stopped, could be checked. In the meantime these same underground explosions, together with a lot of added ideas and added work, has led to a completely new concept: the peaceful uses of nuclear explosives.