generally increased amplitudes, longer periods, and generally longer durations. In addition, the megaton explosions had been characterized by a dispersive train of acoustic waves similar to those produced by the great Siberian meteor and not previously observed from man-made explosions. Operation Castle presented an opportunity to study a wide range of yields, offering a possibility of establishing a lower limit of yield required to generate dispersive waves in the atmosphere. For Castle, the primary objectives were to (1) record and analyze the airborne acoustic waves generated by thermonuclear explosions, in order to provide calibration data for use in the interpretation of the acoustic gignal from foreign explosions and (2) delineate the capabilities and limitations of standard detection equipment and study the relation uf various signal characteristics to the total energy rcleased in the explosion. A secondary objective was to collect data on the propagation of dispersive waves from a very-large atmospheric pressure pulse, with a hope of eventual interpretation in terms of the temperature and wind structure in the upper atmosphere. 7.2.1 Detection Ranges. Each shot (1, 2, 4, 5, 6); in the megaton range was detected withstandard equipment at very-great distances: (1) Every operative station detected the direct wave! from the megaton-range shots. (2) Four of the nine operational stations oa Shot 1 detected the wave via the antipodes’, seven of eleven on Shot 2, four of eleven on Snot 4, eight of eleven on Shot 5, and two of eleven on Shot 6. (3) Four stations de- tected the second passage of the direct wave on Shot 1, three on Shot 2, two on Shot 4, two on Shot 5, and none on Sho: 6. (4) One station detected possible second antipodes arrival trom Shots 4 and &. Maximum detection ranges with standard equipment were 51,470 km for Shot 1, 46,940 Km for Shot 2, 75,200 km for Shots 4 and 5, and 32,080 km for Shot 6. Only four standard-equipment stations detected the direct wave from Shot 3, and the maximum detection range was 11,470 km. None of the stations to the west of the explosion dctected the acoustic waves from Shot 3, although three stations were arrayed betwee. 3,960 and 4,860 km from the explosion. Detection ranges for very-low-frequency (VLF) equipment were generally less than for the standard equipment because of the greater noise recorded on the VLF equipment. Nevertheless, every operational VLF station detected the direct wave from the four highes:-yield shots (1, 2, 4, and 5); most detected Shot 6, but only one detected Shot 3. Maximum detection ranges were 31,590 km for Shot 1; 25,140 km for Shots 2, 4, and 5; 4,040 km for Shot 3; and 18,190 km for Shot 6. These results confirmed thcse obtained from Ivy and previous nuclear d tonations regarding the range of detection. With standard equipment, it was possible to detect megaton snots at very-great distunces (usually at least 25,000 km). Ranges for VLF equipment, while still considerable, were generally oppreciably less than for standard equipment. Range for Shot 3 was greatly reduced, but was greater than the 4,000 km normally considered desirable for effective detection-net operations. 7 2.2 Signal Characteristics. All VLF recordings from megaton shots showed the dispersive train of waves. However, each shot produced significant differences in the variations in period and amplitude with time. Significant changes in the dispersive train ‘The direct wave refers to the signal arriving by the most direct great-circle path from the explosionsite. * The antipodes wave refers to the arrival via the antipodes of the explosionsite. 95