effort; its deputy director Duncan MacDougall also took charge of the Manhattan Project's Project Q. Kistiakowsky replaced Neddermeyer as head of E (for explosives) Division in February 1944. The implosion program acquired a new urgency after Emilio Segrè's group at Los Alamos verified that plutonium produced in the nuclear reactors contained plutonium-240, which made it unsuitable for use in a gun-type weapon. A series of crisis meetings in July 1944 concluded that the only prospect for a working plutonium weapon was implosion. In August, Oppenheimer reorganized the entire laboratory to concentrate on it. A new explosives group, X Division, was created under Kistiakowsky to develop the lenses. Under Kistiakowsky's leadership, X-Division designed the complex explosive lenses needed to compress the fissile plutonium pit. These employed two explosives with significantly different velocities of detonation in order to produce the required waveform. Kistiakowsky chose Baratol for the slow explosive. After experimenting with various fast explosives, X-Division settled on Composition B. Work on molding the explosives into the right shape continued into 1945. The lenses needed to be flawless, and techniques for casting Composition B and Baratol had to be developed. The ERL managed to accomplish this by devising a procedure for preparing Baratol in a form that was easy to cast. In March 1945, Kistiakowsky became part of the Cowpuncher Committee, so-called because it rode herd on the implosion effort. On July 16, 1945, Kistiakowsky watched as the first device was detonated in the Trinity test. A few weeks later, a Fat Man implosion-type nuclear weapon was dropped on Nagasaki. Along with his work on implosion, Kistiakowsky contributed to skiing in Los Alamos by using rings of explosives to fell trees for a ski slope — leading to the establishment of Sawyer's Hill Ski Tow Association. He divorced Hildegard in 1942 and married Irma E. Shuler in 1945. They were divorced in 1962, and he married Elaine Mahoney. White House service In 1957, during the Eisenhower Administration, Kistiakowsky was appointed to the President's Science Advisory Committee, and succeeded James R. Killian as chairman in 1959. He directed the Office of Science and Technology Policy from 1959 to 1961, when he was succeeded by Jerome B. Wiesner. In 1958, Kistiakowsky suggested to President Eisenhower that inspection of foreign military facilities was not sufficient to control their nuclear weapons. He cited the difficulty in monitoring missile submarines, and proposed that the arms control strategy