 Robert F. Christy from the T-1 Group provided support with the theoretical calculations, in particular, a calculation of the critical mass.He calculated that 600 grams of uranium-235 would form a critical mass in a tamper of infinite size.Initially it was planned to operate the Water Boiler at 10 kW, but Fermi and Samuel K. Allison visited in September 1943, and went over the proposed design.