 From August 1944 Fuchs worked in the Theoretical Physics Division at the Los Alamos Laboratory, under Hans Bethe. His chief area of expertise was the problem of imploding the fissionable core of the plutonium bomb. At one point, Fuchs did calculation work that Edward Teller had refused to do because of lack of interest. He was the author of techniques (such as the still-used Fuchs-Nordheim method) for calculating the energy of a fissile assembly that goes highly prompt critical, and his report on blast waves is still considered a classic. Later, he also filed a patent with John von Neumann, describing a method to initiate fusion in a thermonuclear weapon with an implosion trigger. Fuchs was one of the many Los Alamos scientists present at the Trinity test. Bethe considered Fuchs "one of the most valuable men in my division" and "one of the best theoretical physicists we had."
