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.
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
Public domain image from Wikipedia.
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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 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, 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]
- 99 shelter occupants at shelters 9,150 meters north, south, and west of ground zero
- 144 to 160 officers and enlisted men of the evacuation detachment, located 14 kilometers northwest of ground zero near Guard Post 2
- Five radiological safety monitors assigned to the evacuation detachment to perform offsite monitoring of nearby towns and residences
- One radiological safety monitor assigned to Guard Post 4
- Two military policemen at each of the seven guard posts.
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]
SOURCES CITED ON THIS PAGE
[1. Aebersold, Paul. July 16th Nuclear Explosion-Safety and Monitoring of Personnel (U). Los Alamos Scientific Laboratory, Atomic Energy Commission. Los Alamos, NM.: LASL. LA-616. January 9, 1947. 170 Pages.]
[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.]
[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.]
[10. Hempelmann, L. H., M.D. {Extracts from: “Preparation and Operational Plan of Medical Group (TR-7) for Nuclear Explosion 16 July 1945.”} Los Alamos Scientific Laboratory, Atomic Energy Commission. Los Alamos, NM.: LASL. LA-631(Deleted). June 13, 1947. 32 Pages.]
[12. Lamont, Lansing. Day of TRINITY. New York, NY.: Atheneum. 1965. 331 Pages.]
[13. Los Alamos Scientific Laboratory, Public Relations Office. “Los Alamos: Beginning of an Era, 1943-1945.” Atomic Energy Commission. Los Alamos, NM.: LASL. 1967. 65 Pages.]
[14. Oppenheimer, J. R. Memorandum for Group Leaders, Subject: TRINITY Test. Los Alamos Scientific Laboratory. Los Alamos, NM. June 14, 1945. 2 Pages.]
[15. Palmer, T. O., Maj., USA. Evacuation Detachment at TRINITY. {Manhattan Engineer District, Army Corps of Engineers.} {Los Alamos, NM.} {18 July 1945.} 2 Pages.]
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