4.8 OPERATION IVY. IVY, conducted at Enewetak Atoll during autumn 1952, consisted of two detonations. These two detonations, identified in the following table, were the largest nuclear explosions up to that time: Event Date Type Yield 10.4 megatons MIKE 1 November Surface KING 16 November Airdrop 500 kilotons The description of the MIKE detonation by the author of History--Task Group 132.1 and reproduced in History of Operation IVY bears repeating (10: 1,187): The Shot, as witnessed aboard the various vessels at sea, is not easily described. Accompanied by a brilliant light, the heat wave was felt immediately at distances of thirty to thirty-five miles. The tremendous fireball, appearing on the horizon like the sun when half-risen, quickly expanded after a momentary hover time and appeared to be approximately a mile in diameter before the cloud-chamber effect and scud clouds partially obscured it from view. A very large cloudchamber effect was visible shortly after the detonation and a tremendous conventional mushroom-shaped cloud soon appeared, seemingly balanced on a wide dirty stem. Apparently, the dirty stem was due to the coral particles, debris, and water which were sucked high into the air. Around the base of the stem, there appeared to be a curtain of water which soon dropped back around the area where the island of Elugelab [Eluklab] had been. Figure 10 presents a photograph of the MIKE cloud (C). 4.8.1 Background and Objectives of Operation IVY. President Truman made the decision to pursue the development of thermo- nuclear weapons in 1950. Operation GREENHOUSE was an initial step toward this end, as section 4.5 explains. Operation IVY considerably extended the 94