After discussions with JIF SEVEN operations planners, it was decided that a secure voice facility between the ESTES and the firing bunker on Enyu wovnld be of benefit. NSA agreed to provide four sets of AFSAY 804 (x) if the Task Force would send four well qualified radio technicians for ciphony maintenance training and the operation of a test circuit in the Washington, D. C., area. This was accomplisned and the test circuit was successful. NSA approved the facility for operation through TOP SECRET. B. On-Site Phase. The cen-site period proved the extensiveness and the flex- ibility of the communications planning. The significant difficul- ties were successfully overcome and in ne case did communications inadequacies or failures delay the completion of the cverall CASTLE mission. Detonaticn of the first device had an effect on the comm~ nications plan but a swift adjustment to the altered concept was accomplished. The following narrative treats these difficulties which were of the greatest concern, communications-wise, during the CASTLE on-site phase. During the early operational period the Eniwetok-Los Alamos radio-teletype circuit was placed in operation twenty-four hours a day, in contrast to the ten-hour a day operation previously employed. Contimious operation of this circuit soon revealed the unreliability of circuit operation during periods of propagation instability. The unstable conditions most generally existed during critical operational periods, resulting in high precedence traffic