was made for security of the Operation; and to take necessary advance action on anticipated operational problems 50 that the effort during the operational period could be directed toward other matters as they arose. At a conference held during OPERATION IVY, a concept of OPERATION CASTLE was established, proposing a maximum of two very high yield tests and two tests of high yield, with one very high yield device to be detonated at Bikini and the others at Eniwetok. operational period was scheduled for the fall of 1953. The Based on this concept, program and construction planning were initiated in October 1952. Success of IVY tests and projection of these re- sults into the development program prompted the Los Alamos Scientific Laboratory to recommend on 28 November 1952, that CASTLE be expanded to include six tests and that the operational period be delayed from fall 1953 to early spring 1954. This proposal was accepted and on 16 December 1952, Task Group 7.1 issued an "Operational Concept of Castle" which was usable for planning purposes. At this time, the plan for utilizing barges as zero stations for some test devices was proposed. In October of 1953 a seventh test was added to the Operation. _ Aside from the construction and operation of base facilities to accommodate the operational task force eat the various locations, major effort of TG 7.5 was directed toward construction of the nu- merous Scientific Stations and their many inter-related facilities. Extensive changes in plans of the Scientific Task Group as to de- vices to be tested, location of tests, and whether based on barge -6Copteasp OE LANL, +O,