At shot-time, the temperature was 21.8 degrees Celsius, and the
surface 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