ve te RS \ soem, x ABSTRACT Measurements of blast overpressure and thermal-radiation flux were carried out at high altitudes during both Mike and King shots of Operation Ivy by means of parachute-borne telemetering canisters. For each shot six canisters were dropped from each of two B-29 aircraft. Telemetered data were recorded from 10 of the 12 canisters at Mike shot and from 8 of the 12 canisters at King shai. When corrected for known altitude effects, the peak overpressures observed at high altitudes agree well with those measured on the ground except at extreme ranges, where the ground overpressureis relatively tow. It is believed that this is due to upward refraction of the blast wave, which is to be expected at very low overpressures. The observed peak overpressures also agree reasonably well with a peak overpressure vs slant range curve scaled up from Operation Tumbler-Snapper results, but, to obtain agreement with the reported energy yields, the blast efficiency of Mike shot appears to have been about 23 per cent and of King shot about 44 per cent greater than the average of the Tumbler-Snapper shots. The interpretation of the thermal-radiation data is ques*ionable since the observed values are very low as compared to other measurements. It is believed that this is due to cooling of the hot thermocouple junction by ventilation. If sim“ar mea.urements are made in future tests, it is suggested that a shielded thermocouple be used. \\ RESTRICTED DATA QM SECURITY INFORMATION