Project Trinity 1945-1946 | Page 4

a nuclear weapon.
The TRINITY nuclear device was detonated on a 100-foot tower on the
Alamogordo Bombing Range in south-central New Mexico at 0530
hours on 16 July 1945. The nuclear yield of the detonation was
equivalent to the energy released by detonating 19 kilotons of TNT. At
shot-time, the temperature was 21.8 degrees Celsius, and surface air
pressure was 850 millibars. The winds were nearly calm at the surface;
at 10,300 feet above mean sea level, they were from the southwest at 10
knots. The winds blew the cloud resulting from the detonation to the
northeast. From 16 July 1945 through 1946, about 1,000 military and
civilian personnel took part in Project TRINITY or visited the test site.
The location of the test site and its major installations are shown in the
accompanying figures.
Military and Scientific Activities
All participants in Project TRINITY, both military and civilian, were
under the authority of the MED. No military exercises were conducted.
The Los Alamos Scientific Laboratory (LASL), which was staffed and
administered by the University of California (under contract to the
MED), conducted diagnostic experiments. Civilian and military
scientists and technicians, with assistance from other military personnel,
placed gauges, detectors, and other instruments around ground zero
before the detonation. 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. At least 94 of these personnel
were from the Provisional Detachment Number 1, Company "B," of the
9812th Technical Service Unit, Army Corps of Engineers. Military
police cleared the test area and recorded the locations of all personnel
before the detonation.
A radiological monitor was assigned to each of the three shelters,
which were located to the north, west, and south of ground zero. Soon
after the detonation, the monitors surveyed the area immediately

around the shelters and then proceeded out the access road to its
intersection with the main road, Broadway. Personnel not essential to
postshot activities were transferred from the west and south shelters to
the Base Camp, about 16 kilometers southwest of ground zero.
Personnel at the north shelter were evacuated when a sudden rise in
radiation levels was detected; it was later learned that the instrument
had not been accurately calibrated and levels had not increased as much
as the instrument indicated. Specially designated groups conducted
onsite and offsite radiological surveys.
Safety Standards and Procedures
The safety criteria established for Project TRINITY were based on
calculations of the anticipated dangers from blast pressure, thermal
radiation, and ionizing radiation. The TR-7 Group, also known as the
Medical Group, was responsible for radiological safety. A limit of 5
roentgens of exposure during a two-month period was established.
The Site and Offsite Monitoring Groups were both part of the Medical
Group. The Site Monitoring Group was responsible for equipping
personnel with protective clothing and instruments to measure radiation
exposure, monitoring and recording personnel exposure according to
film badge readings and time spent in the test area, and providing for
personnel decontamination. The Offsite Monitoring Group surveyed
areas surrounding the test site for radioactive fallout. In addition to
these two monitoring groups, a small group of medical technicians
provided radiation detection instruments and monitoring.
Radiation Exposures at Project TRINITY
Dosimetry information is available for about 815 individuals who
either participated in Project TRINITY activities or visited the test site
between 16 July 1945 and 1 January 1947. The listing does not indicate
the precise military or unit affiliation of all personnel. Less than six
percent of the Project TRINITY participants received exposures greater
than 2 roentgens. Twenty-three of these individuals received exposures
greater than 2 but less than 4 roentgens; another 22 individuals received
between 4 and 15 roentgens.

PREFACE
From 1945 to 1962, the U.S. Government, through the Manhattan
Engineer District (MED) and its successor agency, the Atomic Energy
Commission (AEC), conducted 235 tests of nuclear devices at sites in
the United States and in the Atlantic and Pacific Oceans. In all, an
estimated 220,000 Department of Defense (DOD)* participants, both
military and civilian, were present at the tests. Project TRINITY, the
war-time effort to test-fire a nuclear explosive device, was the first
atmospheric nuclear weapons test.
* The MED, which was part of the Army Corps of Engineers,
administered the U.S. nuclear testing program until the AEC came into
existence in 1946. Before DOD was established in 1947, the Army
Corps of Engineers was under the War Department.
In 1977, 15 years after the last above-ground nuclear weapons test, the
Centers for Disease Control** noted a possible leukemia cluster among
a small group of soldiers present at Shot SMOKY, a test of Operation
PLUMBBOB, the series of atmospheric