* the Air ‘lasK .A Group 7.4, was based at Kwajalein, some 360 miles from Eniwetok, its mobility and ever-present aircraft prevented the feeling of separation. This was due in part, too, to the presence of the Commander, Air Forces, Joint Task, Force Seven, on the Command Ship. The major elements of the Naval Task Group arrived with the Task Force Headquarters. Approximately one month of preparation was available before the first test was scheduled. During the first part of this remaining month communications had to be tied into all operating areas from the ships. During the period prior to the fist test, operating units devised and perfected their operating plans based on the requirements of the Scientific Operating Plan: The Scientific Operating Plan was a completely detailed plan for the day-to-day conduct of the scientific operations. These plans served to crystallize the concept of operations more clearly for operating personnel. One of the problems that still remained to be solved was that of determining the time of detonation, or H-Hour, in relation to dawn. During the latter part of March this problem was resolved. The requirements were simple. The pilots who would operate the drone aircraft from the mother aircraft had to have sufficient light to permit proper control of the drones as they made their passes into the radio-active cloud. Dr. Froman, the Scientific Director, however, required a minimum of light for one important experiment. The time of the shots was a compromise between these two conflicting requirements. It had been observed that at an altitude of approximately 20,000 feet it was light about , 10 minutes earlier than on the ground. On several mornings B-17 aircraft operated over the test area to determine the visibility at specific times and at the various altitudes at which the drones would operate. On 22 March General Kepner flew over the area with the Commanding Officer of the drone unit, Colonel Kilgore, in an attempt to determine the earliest time at which a successful drone operation would be feasible. Simultaneously, Captain Russell and Dr. Froman on the GSS Albemarle, and Colonel Grills on the USS Mount McKinley observed the light conditions on the surface. The effect of light at ground level at this time on the