While the Comission was planning the 1954 series the Soviet Union announced the explosion of a hydrogen barb. Actually the Russians had probably Getonated a large fission weapon which burned some thermmuclear fuel. For security reasons the Commission could not explain that the Soviets hardly had a deliverable thermonuclear weapon .2° To most Americans the Cammission had to work even harder so as not to lose ‘the grim race with the Soviet Union. The 1954 spring Pacific tests series, called Castle, provided perhaps the greatest technical successes of any tests other than Trinity or Mike. Six thermonuclear shots were fired and most of these surpassed the Commission's most optimistic predictions. Not only did the Canmis- sion have a deliverable thermonuclear weapon but it also could produce a whole "family" of thermonuclear weapons in a spectrum of yields from small tactical to large strategic weapons. Now the Cammission could use a whole new philosophy in building the stockpile. Rather than build bombs with a balanced distribution of yields, the Commission concentrated on making specific types of weapons characteristics into them. >+ Castle, however, and working | unexpectedly demonstrated that optimm | multi-megatcn thermonuclear weapons also could produce significant amounts of deadly fallout. The first shot,of the series, a fifteen megaton blast called Bravo, produced a massive fallout cloud which rose more than twenty miles into the stratosphere and triggered thunderstorms and rain squalls throughout the Pacific test area. Fallout from the cloudwas scattered over more than seven thousand square miles of ocean, the naval task 15