A Pre-Test Explosion

Three shelters, located approximately 9,150 meters (10,000 yards) north, west, and south of ground zero, were built for the protection of test personnel and instruments.

Continuing The First Atomic Bomb,
our selection from Project Trinity 1945-1946 by Carl Maag and by Steve Rohrer published in 1982. The selection is presented in nine installments for 5-minute daily reading. For works benefiting from the latest research see the “More information” section at the bottom of these pages.

Previously in The First Atomic Bomb.

Time: July 16, 1945
Place: Old McDonald Ranch House, New Mexico

1.2 The Project Trinity Site

The TRINITY site was chosen by Manhattan Project scientists after thorough study of eight different sites. The site selected was an area measuring 29 by 39 kilometers* in the northwest corner of the Alamogordo Bombing Range. The Alamogordo Bombing Range was located in a desert in south-central New Mexico called the Jornada del Muerto (“Journey of Death”). The site was chosen for its remote location and good weather and because it was already owned by the Government. MED obtained permission to use the site from the Commanding General of the Second Air Force (Army Air Forces) on 7 September 1944. [12]

[* Throughout this report, surface distances are given in metric units. The metric conversion factors include: 1 meter = 3.28 feet; 1 meter = 1.09 yards; and 1 kilometer = 0.62 miles. Vertical distances are given in feet; altitudes are measured from mean sea level, while heights are measured from surface level, unless otherwise noted.]

Ground zero for the TRINITY detonation was at UTM coordinates 630266.** Three shelters, located approximately 9,150 meters (10,000 yards) north, west, and south of ground zero, were built for the protection of test personnel and instruments. The shelters had walls of reinforced concrete and were buried under a few feet of earth. The south shelter was the Control Point for the test. [12] The Base Camp, which was the headquarters for Project TRINITY, was located approximately 16 kilometers southwest of ground zero. The principal buildings of the abandoned McDonald Ranch, where the active parts of the TRINITY device were assembled, stood 3,660 meters southeast of ground zero. Seven guard posts, which were simply small tents or parked trucks like the ones shown in figures 1-3 and 1-4, dotted the test site. [9]

[** Universal Transverse Mercator (UTM) coordinates are used in this report. The first three digits refer to a point on an east- west axis, and the second three digits refer to a point on a north-south axis. The point so designated is the southwest corner of an area 100 meters square.]

1.3 The Project Trinity Organization

The organization that planned and conducted Project TRINITY grew out of the X-2 Group. LASL, though administered by the University of California, was part of the Manhattan Project, supervised by the Army Corps of Engineers Manhattan Engineer District. The chief of MED was Maj. Gen. Leslie Groves of the Army Corps of Engineers. Major General Groves reported to both the Chief of Engineers and the Army Chief of Staff. The Army Chief of Staff reported to the Secretary of War, a Cabinet officer directly responsible to the President. Figure 1-5 outlines the organization of Project TRINITY.

The director of the Project TRINITY organization was Dr. Kenneth Bainbridge. Dr. Bainbridge reported to Dr. J. Robert Oppenheimer, the director of LASL. A team of nine research consultants advised Dr. Bainbridge on scientific and technical matters. [3]

The Project TRINITY organization was divided into the following groups: [3]

• The TRINITY Assembly Group, responsible for assembling and arming the nuclear device
• The TR-1 (Services) Group, responsible for construction, utilities, procurement, transportation, and communications
• The TR-2 Group, responsible for air-blast and earth-shock measurements
• The TR-3 (Physics) Group, responsible for experiments concerning measurements of ionizing radiation
• The TR-4 Group, responsible for meteorology
• The TR-5 Group, responsible for spectrographic and photographic measurements
• The TR-6 Group, responsible for the airblast-airborne condenser gauges
• The TR-7 (Medical) Group, responsible for the radiological safety and general health of the Project TRINITY participants.

Each of these groups was divided into several units. Individuals were also assigned special tasks outside their groups, such as communications and tracking the TRINITY cloud with a searchlight. [3]

1.4 Military and Civilian Participants in Project Trinity

From March 1944 until the beginning of 1946, several thousand people participated in Project TRINITY. These included not only the LASL scientists, but also scientists, technicians, and workmen employed at MED installations throughout the United States. According to entrance logs, film badge data, and other records, about 1,000 people either worked at or visited the TRINITY site from 16 July 1945 through 1946. [1; 3; 8; 15; 16]

Although supervised by Major General Groves and the Army Corps of Engineers, many Manhattan Project personnel were civilians. Military personnel were assigned principally to support services, such as security and logistics, although soldiers with special skills worked with the civilians (7; 12). Most of the military personnel were part of the Army Corps of Engineers, although Navy and other Army personnel were also assigned to the project. [4; 12]

Chapter 2 The Activities at Project Trinity

The TRINITY nuclear device was detonated on a 100-foot tower at UTM coordinates 630266 on the Alamogordo Bombing Range, New Mexico, at 0530 Mountain War Time, on 16 July 1945. The detonation had a yield of 19 kilotons and left an impression 2.9 meters deep and 335 meters wide. The cloud resulting from the detonation rose to an altitude of 35,000 feet. [5]

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]

SOURCES CITED ON THIS PAGE

[2. Bainbridge, K. T. Memorandum to All Concerned, Subject: TR Circular No. 18–Total Personnel at TR. [Base Camp, Trinity Site: NM.] July 3, 1945. 1 Page.]

[3. Bainbridge, K. T. TRINITY. Los Alamos Scientific Laboratory. Los Alamos, NM.: LASL, LA-6300-H and Washington, D. C.: GPO. May 1976. 82 Pages.]

[4. Bramlet, Walt. Memorandum for Thomas J. Hirons, Subject: DOD Participants in Atmospheric Tests, wo/encl. Los Alamos Scientific Laboratory. Los Alamos, NM. ISD-5. February 20, 1979. 4 Pages.]

[5. General Electric Company–TEMPO. Compilation of Local Fallout Data from Test Detonations 1945-1962. Vol. 1: “Continental US Tests.” Washington, D. C.: Defense Nuclear Agency. DNA 1251-1(EX.). 1979. 619 Pages. (A99) AD/AO79 309.]

[8. Headquarters, 9812th Technical Service Unit, Provisional Detachment No. I (Company “B”). {Extract from: Daily Diary, Provisional Detachment No. 1 (Company “B”), 9812th Technical Service Unit.} Army Corps of Engineers, Department of War. {Santa Fe, NM.} 14 July 1945. 2 Pages.]

[9. Headquarters, Special Service Detachment. Supplemental Special Guard Orders, with Appendix. Los Alamos Scientific Laboratory, Manhattan Engineer District. {Alamogordo, NM.} 14 July 1945. 4 Pages.]

[12. Lamont, Lansing. Day of TRINITY. New York, NY.: Atheneum. 1965. 331 Pages.]

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