experiments. Before the detonation, civilian and military scientists and technicians, assisted by other military personnel, placed gauges, detectors, and other instruments around ground zero. Four offsite monitoring posts were established in the towns of Nogal, Roswell, Socorro, and Fort Sumner, New Mexico. An evacuation detachment consisting of 144 to 160 enlisted men and officers was established in case protective measures or evacuation of civilians living offsite became necessary. Such action was not deemed necessary, however, and the evacuation detachment was dismissed late on the day of the detonation for return to Los Alamos (1: 1). For the detonation, at least 263 DOD participants were at the test site. Among this group were 99 personnel occupying shelters approximately 9,175 meters north, south, and west of ground zero. No one was closer to ground zero at shot-time (1: 31). To determine the extent of the radiation resulting from the detonation, a network of detectors with remote read-out was installed along routes between ground zero and each shelter. In addition, trained monitors with portable radiation survey instruments were assigned to each shelter. detected at the south and west shelters. No radiation was The remote detectors north of ground zero indicated that the radioactive cloud was moving in that direction, and a monitor in the north shelter observed a sharp increase in the radiation level. The shelter was consequently evacuated shortly after the detonation. It was learned later that the monitor had inadvertently changed an adjustment on his instrument, which resulted in a false reading. Very little contamination occurred at the north shelter (1: 1,2). A substantial amount of activity took place at the test site during the first 3 days following the detonation, as scientists entered the ground zero area to retrieve instruments or to perform experiments. Their entry into, activities at, and exit from the test site were carefully controlled. When the itinerary indicated operations in regions of known radiation intensity, a limit was set on the time spent in the area. Radiation detectors were provided, when possible, to permit continuous monitoring of the exposure. Film badges were also provided to each person for subsequent determination and recording of the doses received. The number of personnel at the TRINITY test 72