FOREWORD Operation CASTLE was, in almost every sense of the word, an extension of Operation IVY. Except for the establishment of Joint Task Force SEVEN as a permanent organization and the formation of a fifth task group, very few changes occurred between the two tests which were separated only by a period of about fourteen months. The cut-off date for IVY and the beginning date for CAS~ TLE were the matter, so to speak, of settling on an arbitrary date of 1 January 1953. Since an extensive and detailed history of Op- eration IVY had been written and published, it was decided early in CASTLE planning that the CASTLE history would follow a differem orientation, Joint task forces have been conducting atomic tests in the Pacific since the end of World War II. By the time of CASTLE, these successive operations had been rather thoroughly documented by the individual histories which had been written. Eneugh experience and a wide enough variation of operational contingencies had been encountered to suggest certain major prob- lems common to all atomic task forces, With this in mind, the CASTLE history is for the most part an attempt to point up broadiy those general problems which any task force may anticipate. In addition, though not in the detailed narrative form of previous histories, a treatment of the major difficulties encountered during CASTLE is included. For these reasons, any detailed study of this effort should be made in conjunction with those of previous over- seas tests, particularly GREENHOUSE and IVY. iv