Project Trinity 1945-1946 | Page 9

and Guard Post 7 personnel in the north shelter. The
military police of Guard Post 8 remained at that post, 400 meters east
of the Base Camp (9).
An evacuation detachment of between 144 and 160 officers and
enlisted men was stationed near Guard Post 2, about 14 kilometers
northwest of ground zero. These men were on standby in case ranches
and towns beyond the test site had to be evacuated. Five radiological
safety monitors were assigned to this detachment. Ninety-four men of
the evacuation detachment belonged to Provisional Detachment
Number 1, Company "B," of the 9812th Technical Service Unit, Army
Corps of Engineers, from LASL. The identity of the remaining
evacuation personnel has not been documented (3; 4; 8; 10; 15).
With the exception of the shelter occupants (99 personnel) and
evacuation detachment (between 144 and 160 men), the number of
personnel at the test site at the time of detonation has not been
documented. Film badge records show that approximately 355 people
were at the test site at some time during 16 July. The shelter occupants
and 44 men of the evacuation detachment are on this list. It has not
been possible to pinpoint the location of many of the remaining
personnel. Some were at the Base Camp or on Compania Hill. Since
many of these people returned to the test site after shot-time to work on
experiments, their film badges registered exposures from residual
radioactivity on 16 July. Based on the documented personnel totals, at
least the following 263 individuals were at the test site when the device
was detonated (1; 4; 8-10; 13; 15):
o 99 shelter occupants at shelters 9,150 meters north, south, and west of
ground zero
o 144 to 160 officers and enlisted men of the evacuation detachment,
located 14 kilometers northwest of ground zero near Guard Post 2
o Five radiological safety monitors assigned to the evacuation
detachment to perform offsite monitoring of nearby towns and
residences

o One radiological safety monitor assigned to Guard Post 4
o Two military policemen at each of the seven guard posts (indicated
by photographs such as figures 1-3 and 1-4).
2.2 DETONATION AND POSTSHOT ACTIVITIES
Because of bad weather, the Project TRINITY director (Dr. Bainbridge)
delayed the detonation, which had been scheduled for 0400 hours. By
0445, however, the forecast was better, and shot-time was set for 0530.
This gave the scientists 45 minutes to arm the device and prepare the
instruments in the shelters. The final countdown began at 0510, and the
device was detonated at 0529:45 Mountain War Time from the Control
Point in the south shelter (3; 12).
No one was closer than 9,150 meters to ground zero at the time of the
detonation. With the exception of a few men holding the ropes of
barrage balloons or guiding cameras to follow the fireball as it
ascended, all shelter personnel were in or behind the shelters. Some left
the shelters after the initial flash to view the fireball. As a precautionary
measure, they had been advised to lie on the ground before the blast
wave arrived. Project personnel located beyond the shelters, such as at
the Base Camp and on Compania Hill, were also instructed to lie on the
ground or in a depression until the blast wave had passed (1). However,
the blast wave at these locations was not as strong as had been
expected.
In order to prevent eye damage, Dr. Bainbridge ordered the distribution
of welder's filter glass. Because it was not known exactly how the flash
might affect eyesight, it was suggested that direct viewing of the
fireball not be attempted even with this protection. The recommended
procedure was to face away from ground zero and watch the hills or
sky until the fireball illuminated the area. Then, after the initial flash
had passed, one could turn around and view the fireball through the
filter glass. Despite these well-publicized instructions, two participants
did not take precautions. They were temporarily blinded by the intense
flash but experienced no permanent vision impairment (1; 17).

People as far away as Santa Fe and El Paso saw the brilliant light of the
detonation. Windows rattled in the areas immediately surrounding the
test site, waking sleeping ranchers and townspeople. To dispel any
rumors that might compromise the security of Project TRINITY, the
Government announced that an Army munitions dump had exploded.
However, immediately after the destruction of Hiroshima, the
Government revealed to the public what had actually occurred in the
New Mexico desert (12; 13).
Immediately after the shot, Medical Group personnel began the
radiological monitoring activities described in section 3.1.2. At 0815,
when most of the monitoring activities were completed, preparations
began for entrance into the ground zero area. To regulate entry into the
area, a "Going-in Board" was established, consisting of Dr. Bainbridge,