the series consisted of four tower shots, two at 200 feet and two at 300 feet (7: 1): Event DOG EASY GEORGE ITEM Date Type Yield (kilotons) 8 April Tower NA* 21 April Tower 47 9 May Tower NA 25 May Tower NA *Not announced 4.5.1 Background and Objectives of Operation GREENHOUSE. The purpose of the four GREENHOUSE tests was to continue development of nuclear weapons for defense. More specifically, work was proceeding at this time on developing thermonuclear weapons, and the GREENHOUSE tests were part of this process (7: 1). In 1949, the Soviet Union detonated its first atomic bomb, providing the impetus for the United States to proceed with development of a bomb whose energy would come from the fusion, or joining, of light elements. weapon is also called a thermonuclear, or hydrogen, bomb. Such a The Atomic Energy Commission received Presidential approval for work in this area in January 1950 after lengthy debate in high defense circles over the feasibility and advisability of such weapons (7: 21). Although the GREENHOUSE nuclear devices were not thermonuclear devices, two of them involved thermonuclear experiments, and one test, GEORGE, was an important step toward thermonuclear devices. GEORGE demonstrated the initiation of a sustained thermonuclear reaction by use of a fission reaction. This led directly to the first successful thermonuclear test, MIKE (Operation IVY), some 16 months later. In addition, ITEM, the fourth test of the series, involved boosting the efficiency of fission explosions. Development of this experiment had been planned before the Soviet test in 1949 (7: 21). 84