The next party to approach ground zero consisted of a photographer and a radiological safety monitor. Wearing protective clothing and respirators, the two men were about 730 meters northwest of ground zero photographing "JUMBO" from 1100 to 1200 hours. "JUMBO," shown in figure 2-7, was a massive container built to contain the high-explosive detonation of the TRINITY device and to allow recovery of the fissionable material if the device failed to produce a nuclear detonation. The plan to use "JUMBO," however, was abandoned when the scientists concluded that a fairly large nuclear explosion was certain. The container remained on the ground near the shot-tower during the detonation. Both the photographer and the monitor received an estimated radiation exposure between 0.5 and 1 roentgen (1; 7). The last party to "go in" on shot-day consisted of six men retrieving neutron detectors. They entered the test area at 1430 hours. Three of the men went to a point 730 meters south of ground zero to pull out cables carrying neutron detectors located 550 meters south of ground zero. The group wore protective clothing and respirators and spent about 30 minutes in the area. The remaining three men drove as close as 320 meters southwest of ground zero to retrieve neutron detectors. They got out of their vehicle only once, at about 460 meters from ground zero, and spent a total of about ten minutes making this trip through the area. Each man's radiation exposure measured less than 1 roentgen (1). Most of the soldiers of the evacuation detachment remained in their bivouac area near Guard Post 2. According to a report written by the detachment commander, a reinforced platoon was sent to the town of Bingham, about 29 kilometers northeast of the test site, while offsite radiological safety monitors surveyed the area. The evacuation detachment was dismissed at 1300 hours on shot-day when it became evident from offsite monitoring that evacuations would not be undertaken. The detachment returned to LASL at 0400 on 17 July (15). Two B-29 aircraft from Kirtland Field, Albuquerque, New Mexico, participated in post-shot events. Their planned mission was to pass over the test area shortly before the explosion to simulate a bomb drop. After the TRINITY device had been detonated, the aircraft would circle near ground zero, while the men onboard would measure the atmospheric effects of the nuclear explosion. This would enable them to determine whether a delivery aircraft would be endangered. However, because of bad weather on shot-day, Dr. Oppenheimer canceled the aircraft's flight in the ground zero area. Instead, the two B-29s, each with 12 men onboard, flew along the perimeter of the bombing range and observed the shot from a distance of 19 to 29 kilometers. Among those observers was a Navy captain who was also the MED Chief of Ordnance (6; 12; 13). 2.3 ACTIVITIES AFTER 16 JULY 1945