with these measurements the atmospheric attenuation (transmission property) along light paths of interest was studied in order to aid in the interpretation of results. Instrumented bomber-type aircraft were also employed to study, in free air and at altitudes significant to delivery aircraft, the thermal intensity vs time and the associated radiation-induced aircraft- skin temperatures. The latter information is clearly essential to studies of safe aircraft delivery techniques. The instrumentation utilized to accomplish the thermal-radiation measurements included thermocouples, bolometers, photocell-recorder combinations, high-speed spectrographs, and skin patches. Results were, in general, most gratifying, the only serious loss of data occurring in the thermal-radiation project for King Shot. Many data, the quality of which appears to be excellent, were obtained on both shots. A cursory analysis points out the following facts of more or. less general interest: 1. The apparent thermal energy of Mike Shot was at least 0.7 Mt. This value is uncorrected for clouds and dust and hence is somewhat low. 2. On Mike Shot the left wing access door of the B-36D experienced a temperature rise of 93°F. The thickness of the aluminum was 0,025 in., and the aircraft was approximately 15 nautical miles from zero at an altitude of 40,000 ft. This aircraft received a relatively high ther- mal flux of 46.9 Btu/sq ft. The predicted value based on a 6-Mt yield was 36 Btu/sqft. 3. The apparent thermal energy of King Shot was at least 48 kt. 2.9 PROGRAM 9, ELECTROMAGNETIC PHENOMENA This program was concerned with the detection and measurement of various electromagnetic phenomena associated with nuclear detonations. The purpose of one project was a study of the correlation between nuclear-explosion-induced ionospheric disturbances and the inter-ruption of radio communications. Another project was a feasibility study of radar-scope photography as an indirect bomb damage assessment (IBDA) technique. In addition, two projects were concerned with documentation of the broad-band electromagnetic signal given off by the exploding devices, Selected standard radio-frequency (20-kc and 4.215-Mc) bands were of particular interest in one of these projects; the other project was designed to test the feasibility of this technique for making remote diagnostic measurements, and hence the particular interest here was in the early (first few millionths of a second) signal characteristics. The techniques used to obtain data for the detection and measurement of electromagnetic phenomena included air-borne radar-scope photography, the reception and recording of selected radio transmission, and the documentation of ionospheric height and continuity. Quantitative measurements of the gross explosion-induced electromagnetic signal were made possible by first displaying portions of that signal on the faces of cathode-ray tubes. The results of these efforts were excellent. All projects obtained usable data on both shots, the detailed reduction of which is being carried out at present. On Mike Shot the early electromagnetic signal was displayed in sufficient detail to allow a rough measurementof the time delay between primary and secondary fission reactions. A Navy P2V flying 200 miles west of Eniwetok and transmitting a continuous-wave signal to Bikini was able to contact Bikini shortly after M+2 hr, indicating no long-time disruption of the ionosphere. Also, for this shot, the radar-scope photographs show both fireball growth and shock progress. 2.10 PROGRAM 10, TIMING AND FIRING The timing and firing program was primarily one of support rather than experimentation. As its name implies, this program consisted in furnishing the various experimental projects with the required timing signals (for starting equipment, ete.) on both shots and supplying the arming and firing signals to the Mike device. In addition, vital information was telemetered 13