SECTICN I Assignment of the CASTLE Mission to Task Group 7.1, and Transition to IVY A. 1. CASTLE activities at the Los Alamos Scientific Laboratory (LASL) —«a officially began with the activation of Task Group 7.1 (1G 7.1), a part of ‘Joint Task Force SEVEN, on 1 February 1953. Prior to that time a certain anount of general planning had been done as IVY approached completion, and requirements for the next test became evident. These basic requirements were of two kinds, those related to the devices to be testea and those related to the test sites at the Pacific Proving Grounds. 2. During GREENHOUSE, ‘detonations GEORGE and ITEM demonstrated the Ay and seemed to justify further development. During IVY, the MIKE detonation substantiated previous convictions, and, since the device used was a completely experimental contrivance, point- ed out that the development of an emergency capability weapon along the same ; principles was now a requirement. 3. During IVY it was determined that a subsequent test program would be called CASTIZ, that it would occur on an accelerated schedule during early fall 1953, about ten months from IVY instead of the usual longer in-- terin, that it would feature one thermonuclear device and two fission devices, and that it would be located at Enivetok Atoll. h. - , later during Ivy, especianty efter MIKE, the need for changes be- came evident, and the original program was adjusted to occur during early Spring 1954, to include six thermonuclear devices, and to be located at both Eniwetok and Bikini Atolls. Still later, during late summer 1953, a