After Leonard I. Schiff calculated that an initiator could theoretically improve the efficiency of a gun-type fission weapon, Oppenheimer gave approval on 15 March 1945 for initiators to be included in the Little Boy design.
Schiff's calculation suggested that an initiator could potentially improve the efficiency of a gun-type fission weapon, leading Oppenheimer to approve their use in the Little Boy design on 15 March 1945.