In early 1943, Wigner and his Theoretical Group that included Alvin Weinberg, Katharine Way, Leo Ohlinger, Gale Young and Edward Creutz produced a design for a production reactor with water cooling. The choice of water as a coolant was controversial, as it was known to absorb neutrons, thereby reducing the efficiency of the reactor, but Wigner was confident that his group's calculations were correct and that with the purer graphite and uranium that was now available, water would work, while the technical difficulties involved in using helium as a coolant would delay the project.