This forecast is not based on merely guesswork. When we decided to go all out in developing the A-bomb—and we didn’t really go to work in earnest until May 1943—nobody knew that it could be successfully made. There were two enormous major problems to be solved, and solved in time to be of use in winning the war. One was to produce unheard-of quantities of fissionable materials (U-235 and plutonium), literally in quantities billions of times greater than had ever been produced before. Nobody knew whether it could be done or how it could be done. Three gigantic plants were built, at a cost of $1,500,000,000, on the mere chance, “calculated risk” we called it, that one of them would work. As it turned out, they all worked, some more efficiently than others, though all contributed to the shortening of the war. The second major problem, among a host of smaller ones, all important to the successful attainment of the goal, was how to assemble the materials produced in the billion-dollar plants into a bomb that would live up to expectations. Both major problems had to be solved simultaneously. The designing of the bomb went on for more than two years with only trickles of the active material. Yet despite all these enormous difficulties the A-bomb was completed for testing in about two years and three months after the beginning of the large-scale effort. Compared with the enormousness of the problems that had to be solved, and were solved successfully in this remarkably short time, the problems still to be solved for building the hydrogen bomb appear relatively simple, since all the materials required and the plants to produce them are already built, paid for, and operating successfully. As already pointed out, we have the A-bombs to serve as triggers, large stockpiles of deuterium, and the refrigeration equipment and techniques to liquefy it. We have an adequate supply of lithium for the production of tritium, which, as explained earlier, would be used as the extra kindling to the A-bomb match. And we have, of course, our gigantic plutonium factories at Hanford, Washington, in which the lithium could be converted into tritium in the desired amounts. Thus, instead of having to start from scratch as we were forced to do with the A-bomb, we have at hand all the necessary ingredients for the H-bomb with the possible exception of sufficient tritium, and since we have the plutonium plants, greatly expanded and improved since the end of the war, it is reasonable to make a “guestimate,” to use a word popular in wartime, that a few months should suffice for them, if they are employed exclusively for that purpose, to produce tritium in proper amounts.