Project Trinity 1945-1946 | Page 8

air pressure was 850 millibars. Winds at shot-time were nearly calm at
the surface but attained a speed of 10 knots from the southwest at
10,300 feet. At 34,600 feet, the wind speed was 23 knots from the
southwest. The winds blew the cloud to the northeast (5).

2.1 PRESHOT ACTIVITIES
Construction of test site facilities on the Alamogordo Bombing Range
began in December 1944. The first contingent of personnel, 12 military
policemen, arrived just before Christmas. The number of personnel at
the test site gradually increased until the peak level of about 325 was
reached the week before the detonation (2; 12).
On 7 May 1945 at 0437 hours, 200 LASL scientists and technicians
exploded 100 tons of conventional high explosives at the test site. The
explosives were stacked on top of a 20-foot tower and contained tubes
of radioactive solution to simulate, at a low level of activity, the
radioactive products expected from a nuclear explosion. The test
produced a bright sphere which spread out in an oval form. A column
of smoke and debris rose as high as 15,000 feet before drifting eastward.
The explosion left a shallow crater 1.5 meters deep and 9 meters wide.
Monitoring in the area revealed a level of radioactivity low enough to
allow workers to spend several hours in the area (3; 12).
The planned firing date for the TRINITY device was 4 July 1945. On
14 June 1945, Dr. Oppenheimer changed the test date to no earlier than
13 July and no later than 23 July. On 30 June, the earliest firing date
was moved to 16 July, even though better weather was forecast for 18
and 19 July. Because the Allied conference in Potsdam, Germany, was
about to begin and the President needed the results of the test as soon as
possible, the TRINITY test organization adjusted its schedules
accordingly and set shot-time at 0400 hours on 16 July (3; 12; 14).
The final preparations for the detonation started at 2200 on 15 July. To
prevent unnecessary danger, all personnel not essential to the firing
activities were ordered to leave the test site. During the night of 15 July,
these people left for viewing positions on Compania Hill,* 32
kilometers northwest of ground zero. They were joined by several
spectators from LASL (3; 12).
* "Compania" also appears as "Compana," "Campagne," or
"Compagna" in various sources.

Project personnel not required to check instruments within the ground
zero area stationed themselves in the three shelters or at other assigned
locations. The military police at Guard Posts 1, 2, and 4 blocked off all
roads leading into the test site, and the men at Guard Post 8, the only
access to the ground zero area from the Base Camp, ensured that no
unauthorized individuals entered the area (9; 12).
At 0100 hours on 16 July, military policemen from Guard Posts 3, 5, 6,
and 7 met to compare their logs of personnel authorized to be in the
ground zero area. The guards then traveled along the access roads to
clear out all project personnel. As individuals left for their assigned
shelters or stations, their departures from the test area were recorded in
the military police logs. By 0200 the area sweep was completed, and
the military police went to their shelters and stations. A final check of
personnel was made in each shelter (3; 9; 12).
At the time of detonation, 99 project personnel were in the three
shelters: 29 in the north shelter, 37 in the west shelter, and 33 in the
south shelter. Dr. Oppenheimer, Dr. Bainbridge, and other key
personnel awaited the firing at the south shelter, which served as the
Control Point. Figure 2-3 shows the exterior of the south shelter; figure
2-4 gives an interior view of one of the shelters, most likely the south.
Although most of the shelter occupants were civilians, at least 23
military participants were spread among the three shelters (1; 12).
The remainder of the test site personnel were positioned at the Base
Camp 16 kilometers south-southwest of ground zero, or on Compania
Hill, or at the guard posts. Important Government officials, such as
General Groves and Dr. Vannevar Bush, Director of the U.S. Office of
Scientific Research and Development, viewed the detonation from a
trench at the Base Camp. The Base Camp is depicted in figure 2-5.
The military police of Guard Posts 1 and 2 were instructed to be in
foxholes approximately five kilometers west and north, respectively,
from their posts. The military police of Guard Posts 3 and 4 were
instructed to be in foxholes south of Mockingbird Gap. A radiological
safety monitor was assigned to the group from Guard Post 4. Guard
Post 5 personnel were to be in the south shelter, Guard Post 6 personnel

in the west shelter,