Only enough U-235 would be available for one bomb. But if the implosion concept worked, several such bombs might be ready by the end of 1945.
ENOUGH was known about the gun method to justify going ahead without a full test. But the implosion method was still in a preliminary stage; among its problems was that of a firing system that could initiate all the explosive lenses at once. The only idea for doing so was an explosive switch, but that could not be tested without destroying the firing mechanism. Oppenheimer raised the problem in June 1944 at one of his seminars.
After listening to the discussion, I suggested developing triggered spark gaps to act as very rapid switches. They might make it possible to initiate the explosive lenses within a fraction of a microsecond. Oppenheimer told me to get a few people together and work on the idea. By the end of the summer, we had accumulated enough evidence to say that this method was feasible. After much debate and many misgivings, we were given a go-ahead in October to incorporate triggered spark gaps into a firing unit for ''the gadget,'' as the bomb was called.
Many months of work remained before the firing mechanism would be ready. The ''X-unit'' had to initiate at 32 points with astonishing simultaneity. If it did not, the explosive yield would be low.
The full-scale test of the bomb was planned for pre-dawn Mon., July 16, the day before President Harry Truman was to meet with Joseph Stalin and Winston Churchill at Potsdam, Germany. By then, we felt we were ready, but many involved in the project doubted that the complicated implosion-bomb system would work effectively and with a large enough explosive yield. Several days before the firing date, the doubts were exacerbated when heavy clouds passed over the desert test area near Alamogordo, N.M., and an electrical surge set off the X-unit. It would have set off a live bomb.