reel were held down to a bare minimum, with maximum utilization being placed on hard-wire circuits. At Johnston Island this was extremely practical because of its size and the concentration of the scientific stations. A special hard-wire circuit was established from the bunker (J-70) switchboard to all manned stations for muster and coordination of the scientific effort. This circuit proved to be an extremely valuable adjunct to the installed dial system. Interference with scientific instruments from all sources was a continuing problem throughout Hardtack.- Interference sources were determined by means of ECM equipment, logic, visual and audible recognition, and the "cut and try" method. The ECM solution, was of course, the most reliable in that, bearing could be determined and equipment identified by pulse analyzation, but was least effective either due to equipment malfunction or inher- ent equipment design limitations. As a rule normal ECM equipment sensitiv- ity was far below that of the scientific receivers. The solution to this prob- lem was to make the ECM center mobile and "sample" the interference with a probe from the scientific receivers themselves. This approach was tried during the Newsreel phase of the operation and proved to be a valid concept. For future operations involving large scale radio telemetry, the mobile ECM concept should be continued, and the equipment should be of the latest design that can be procured on a loan basis. Further, spare parts should be available in advance to provide maximum flexibility. A source of inde- pendent power should also be provided on a mobile mount. In order to transmit the count-down to all projects over iong distances, it was necessary to install medium high frequency single side-band equipment for the Teak and Orange events. This communications system provided ‘ a more rapid means of notifying the distant stations of delays or holds using WWYV time base. , The single-side band equipment was installed on Sand Island by Task Group 7.5 and operated by Task Unit 5 in the 7 and 14 Mc bands. These frequencies gave extremely good coverage throughout the Pacific, and unofficial reports from amateur operators in Honolulu indicate that the transmissions were received in Alaska, Australia, and throughout the U.S. Due to the variety and types of receivers being used by projects to copy the count-down it was found necessary to instigate a calibration count-down starting at H~-4 hr to enable the users to have their receivers properly tuned. This requirement did not exist before with the VHF count-down equip- ment as these receivers were crystal-controlled and no calibration or tuning count-down was required, 3.14 SECURITY As during previous operations, the security activities of Task Groups 7.1 and 7.5 were joint responsibilities. Within TG 7.1, coordination and establishment of security policies was effected by the Classification Officer, while personnel security functions were delegated to the Military Executive, J-1. Personnel security responsibilities were redelegated to cover the three major groups of participants: Los Alamos (LASL, Sandia, EG&G, and ist RSSU), Livermore (UCRL), and Sandia Base (DWET). Joint Task Force Seven SOP's 205-1 through 205-9, establishing the security policies for Hardtack, were published between October 14 and No105 AFWL/HO quam [04