-llmorning. As the long hours droned on during the night there were frequent formal and informal briefings, as the Air-Weather Service Unit constantly collected and evaluated new data, With continued favorable reports and with the zero hour approaching, decisions had to be made. Mobile monitoring teams had been dispatched during the day and were in the general vicinity of their assigned locations, sary to spot them more definitely. It was now neces- Also, at about this time it was custom- ary for the Liaison Officer of the Federal Aviation Agency, attached to the Test Organization at the Nevada Test Site, to direct the closure of certain air spaces for commercial aircraft from the Site out to specified distances, altitudes and times, principally to avoid the possibility of the flash of the detonation temporarily dazzling the eyes of pilots. Cloud tracker air- craft of the Test Organization were ordered to take off so as to be in position at H-Hour. Helicopter crews were alerted for close-in terrain surveys “%L-20 and C-47 crews for more distant terrain surveys. The usual ground and aerial sweeps had been made in the afternoon to assure there was no unauthorized person in the close-in areas in the direction of the fallout. The technical crews reported their readiness for all experimental work on-site and off-site. DOE ARCHIVES At 0505 Pacific Daylight time, on the morning of May 19, 1953, HARRY was detonated. Within a short time the initial technical data from HARRY shot was collected and most of the scientists went back to camp for a well earned. rest, But not the radiological safety personnel - their day was just beginning.