Operation HARDTACK II

Note: For information related to claims, call the Department of Veterans Affairs (VA) at 800-827-1000 or 

the Department of Justice (DOJ) at 800-729-7327. For all other information, call the Nuclear Test 

Personnel Review (NTPR) Program at 800-462-3683.

Operation HARDTACK II was a series of atmospheric nuclear tests conducted at the Nevada Test Site (NTS) 

from September 19 to October 31, 1958. The operation consisted of 19 weapons tests and 18 safety tests. 

The weapons tests were conducted to evaluate the yield and efficiency of newly developed nuclear devices. 

The safety tests were designed to determine the stability of nuclear devices during transportation and storage. 

HARDTACK II involved an estimated 1,750 Department of Defense (DOD) participants in scientific test 

activities, air support, and administrative staff support.

Historical Background

HARDTACK II was the continental phase of Operation HARDTACK. It followed Operation HARDTACK I, the 

nuclear test series conducted in the Pacific Ocean from April to August 1958. The Atomic Energy Commission 

(AEC), in conjunction with Field Command, Armed Forces Special Weapons Project (AFSWP), the Office of 

Civil and Defense Mobilization (OCDM), and other Government agencies, was involved in the planning for 

HARDTACK II. In August 1958, the President of the United States approved the AEC request to conduct the 

operation. HARDTACK II was the last series before the United States adopted a nuclear testing moratorium, 

which had been originally intended to last one year but continued until 1961. HARDTACK II was designed to:

• Test nuclear devices for possible inclusion in the defense arsenal

• Test safety characteristics of nuclear devices

• Improve containment techniques for underground detonations.

DOD participants were involved in three activities:

• Administrative staff support

• Test group activities

• Air and ground support, including radiological safety monitoring.

DOD personnel assisted the AEC Test Manager in planning, coordinating, and executing the programs and 

activities associated with HARDTACK II. They oversaw the technical and military objectives of the series for 

the DOD. 
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The following five test groups conducted scientific experiments to evaluate effects characteristics of the 

nuclear devices:

• DOD Effects Test Group, AFSWP

• Los Alamos Scientific Laboratory (LASL) Test Group

• University of California Radiation Laboratory (UCRL) Test Group

• Civil Effects Test Group (CETG)

• OCDM Test Group.

The largest number of DOD participants took part in 11 projects conducted by the DOD Effects Test Group. 

Information gained from the projects was used in developing delivery systems for nuclear devices and in 

determining the military requirements for future nuclear device designs. At least one DOD Effects Test Group 

project was conducted at all the weapons tests except Shot BLANCA, the last weapons test of the series. One 

project was also conducted at four of the safety tests: MARS, HIDALGO, NEPTUNE, and VESTA.

Two of the nuclear weapons tests, HAMILTON and HUMBOLDT, were effects tests cosponsored by the DOD

and UCRL, an AEC weapons development laboratory. All 11 DOD Effects Test Group projects were 

performed at HAMILTON, and five were conducted at HUMBOLDT. For the DOD projects conducted only at 

these two shots, personnel placed thermal and radiation measuring instruments and soil samples in foxholes, 

in armored personnel carriers, and along cables between 5 and 730 meters from ground zero to determine the 

radiation and thermal effects produced by low-yield nuclear detonations. Participants also placed pigs and 

mice in the foxholes and armored personnel carriers to obtain data on biological effects of blast, heat, light, 

and radiation from nuclear detonations. Many of the experiments had to be retrieved soon after the 

detonations, while others could be collected later, when radiation intensities had decreased.

The DOD Effects Test Group projects involved personnel from the following service laboratories and agencies:

• Ballistic Research Laboratories

• Chemical Warfare Laboratories

• Chemical Corps Training Command

• Army Chemical Center

• Army Artillery Board

• Engineer Research and Development Laboratories

• Signal Research and Development Laboratories

• Walter Reed Army Institute of Research

• Headquarters, Continental Army Command

• Air Force Special Weapons Center

• Air Force Cambridge Research Laboratories.

The LASL and UCRL Test Groups conducted experiments to obtain information on diagnostic and effects 

characteristics of the devices developed and sponsored by each laboratory. LASL sponsored nine nuclear 

weapons tests and nine safety experiments. UCRL sponsored 10 nuclear weapons tests, including 

2 sponsored with DOD, and 9 safety experiments. 

DOD involvement in LASL and UCRL Test Group projects included cloud-sampling missions conducted by Air 

Force Special Weapons Center (AFSWC) personnel. One AFSWC unit, the 4926th Test Squadron, flew 

aircraft through the clouds at 16 of the nuclear weapons tests and 12 of the safety experiments to collect 

particulate samples of the clouds. The samples aided the laboratories in determining the yield and efficiency 

of each nuclear device.

The CETG and OCDM Test Group conducted projects to determine potential effects of blast, heat, radiation, 

and fallout on civilian populations and structures. Although some DOD personnel were assigned to the 
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agencies and laboratories conducting the projects, there was no documented DOD participation at these 

projects.

DOD personnel participated in air support activities for the Test Manager and the test groups at HARDTACK II. 

AFSWC, located at Kirtland Air Force Base (AFB), New Mexico, provided air support to the Test Manager. 

AFSWC conducted cloud-sampling missions for the UCRL and LASL Test Groups and cloud-tracking 

missions, sample courier missions, aerial terrain surveys, and other air support, as requested by the Test 

Manager.

The 4950th Test Group (Nuclear) was the principal AFSWC unit involved in HARDTACK II. The 4950th

consisted of four squadrons, three of which participated in the operation. The 4926th Test Squadron 

(Sampling) and the 4952nd Support Squadron (Test) were located at Kirtland AFB. The 4935th Air Base 

Squadron was the permanent unit at Indian Springs AFB, Nevada, 30 kilometers east of Camp Mercury, and 

was central to the mission of that base. Other Air Force units involved in HARDTACK II included the 

4900th Air Base Group from Kirtland AFB, elements of the 20th Helicopter Squadron of the Tactical Air 

Command (TAC), and the 865th Air Control and Warning Squadron of the Air Defense Command. The peak 

strength of these air support units during HARDTACK II was approximately 400 personnel.

Summaries of Operation HARDTACK II Nuclear Weapons Tests

The 19 HARDTACK II nuclear weapons tests were conducted in Areas 3, 5, 7, 9, and 12 of the NTS. There 

were 10 balloon, 4 underground, and 5 tower detonations. The accompanying table presents information on 

the nuclear weapons tests, and the accompanying figure indicates their locations.

Eleven of the 19 tests had yields under 1 kiloton. Some of these, including HAMILTON, HUMBOLDT, and 

EVANS, resulted in yields lower than expected. Shot BLANCA produced the largest yield.

BLANCA was detonated on October 30, 1958, in a tunnel 987 feet underground, with a 22-kiloton yield. Some 

radiation vented into the atmosphere producing a cloud that reached 7,700 feet above the ground and drifted 

southwest. DOD participation was limited to cloud-sampling, cloud-tracking, photography, and observer 

missions conducted by AFSWC.

Shots HAMILTON and HUMBOLDT were the two DOD effects tests and had the largest number of DOD

participants. Shot HAMILTON was detonated on October 15, 1958, on a 50-foot wooden tower. The device 

produced a lower-than-expected yield of 0.0012 kiloton. Before the detonation, personnel set up 

instrumentation for 11 DOD Effects Test Group projects. Many of the projects required that instruments be 

placed as close as 4.5 meters to the shot tower. One project was conducted 160 kilometers from the NTS. 

For six of the projects, the same personnel both placed and retrieved the instruments. This reduced the 

number of personnel required to enter the shot area after the detonation. In addition to the DOD Effects Test 

Group projects, AFSWC conducted cloud-sampling, cloud-tracking, sample courier, and terrain survey 

missions. Nine aircraft with 26 AFSWC aircrew personnel conducted these missions.

Shot HUMBOLDT, the second DOD effects test, was conducted on October 29, 1958, at 6:45 a.m. The 

device, detonated on a 25-foot wooden tower, had a yield of 0.0078 kiloton. Personnel placed instruments 

between 9 meters and 2 kilometers from ground zero for all five DOD Effects Test Group projects. For three of 

the projects, personnel worked together to place and retrieve experiments, as they did at Shot HAMILTON. 

Cloud-sampling, cloud-tracking, and sample courier missions were conducted after the detonation. One 

aircraft participated in each of the missions. The missions engaged 10 AFSWC aircrew personnel.

Summary of Operation HARDTACK II Safety Tests

The 18 remaining detonations in HARDTACK II were safety tests conducted to determine the stability of newly 

developed nuclear weapons during transportation and storage. Elements of the conventional high explosive 
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portions of these devices were fired to simulate accidental damage and to determine the potential for such 

partial firings to result in nuclear yield. Data gained from the tests were used to develop devices that could 

withstand shock, blast, fire, and other accidents and produce nuclear yields of less than 4 pounds.

The HARDTACK II safety tests were conducted in Areas 3, 7, 8, 9, and 12 of the NTS. The shots consisted of 

six shaft, three tunnel, one balloon, five tower, and three surface detonations. The safety experiments ranged 

in yield from Shot NEPTUNE, which had a yield of 0.115 kiloton to Shots SAN JUAN, OBERON, and 

GANYMEDE, which had no measurable yield. The accompanying table presents data on the safety tests, and 

the accompanying figure shows their locations. DOD participation in the safety tests was limited to 1 DOD

Effects Test Group project conducted at 4 safety tests, cloud sampling conducted at 12 tests, cloud tracking at 

11 tests, sample courier missions after 7 safety experiments, one aerial photography mission and 1 observer 

mission during the final safety test, TITANIA.

Radiation Protection Standards

The Nevada Test Site Organization and AFSWC developed radiological safety procedures to minimize 

exposure of individuals to ionizing radiation while they accomplished their missions at HARDTACK II. The 

AEC recommended a gamma plus neutron exposure limit of 3 rem∗ per calendar quarter or a total exposure of 

5 rem per year for DOD participants at the operation. This was the accepted occupational limit for gamma 

exposure as recommended by the National Council on Radiation Protection and Measurements.

AFSWC personnel who conducted cloud-sampling missions at HARDTACK II were permitted to receive up to 

10 rem during the series, and those individuals who participated in cloud sampling at both HARDTACK I and 

HARDTACK II were permitted to receive 15 rem during the two series.

The radiological safety procedures at HARDTACK II were essentially the same as those used for Operation 

PLUMBBOB, the series of tests conducted at the NTS in 1957. Personnel from the Radiological Safety 

Division of the Reynolds Electrical and Engineering Company conducted all onsite radiological safety activities 

and functions, including:

• Personnel dosimetry – issuing, exchanging, and developing film badges for participants and 

determining gamma radiation exposures recorded on film badges

• Clothing and equipment – providing anti-contamination clothing and respiratory equipment

• Monitoring – providing radiological survey equipment, performing radiological surveys, and controlling 

access to all radiation areas

• Decontamination – detecting and removing contamination on personnel, vehicles, and equipment.

Personnel from the 4950th Test Group provided radiological safety for AFSWC participants at Indian Springs 

AFB and Kirtland AFB. These responsibilities included monitoring and decontaminating personnel and aircraft.

Radiation Doses at Operation HARDTACK II

HARDTACK II participants wore film badges as a requirement for access to the NTS, and dosimetry records 

were maintained for all participants. Fifteen DOD participants had doses greater than 3 rem (gamma). The 

highest doses, accrued by two Army officers, were between 10 and 11 rem. The totals of film badge and 

 ∗ A rem is a radiation protection unit of measure that quantifies the risk of biological effects resulting from exposure to 

ionizing radiation. Ionizing radiation is any radiation (gamma, x-ray, beta, neutron, or alpha) capable of displacing 

electrons from atoms or molecules, thereby producing ions. According to the National Council on Radiation Protection 

and Measurements (NCRP, Report No. 160, Table 1.1), the general U.S. population receives about 0.62 rem per year 

from natural background radiation sources (radon, cosmic rays, and rocks) and man-made radiation sources (medical 

diagnostic x-rays and consumer products). As a basis of comparison, a standard diagnostic chest x-ray delivers a 

radiation dose of about 0.02 rem.
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reconstructed doses for DOD participants at HARDTACK II are depicted below.

For more information, see the report “Operation HARDTACK II 1958” (DNA6026F), available online at 

https://www.dtra.mil/DTRA-Mission/Reference-Documents/NTPR-Info/

September 2021
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Summary of Operation HARDTACK II Nuclear Weapons Tests (1958)a

Shot Sponsor Planned

Date

Actual 

Date

Local 

Timeb

NTS 

Location Type Height of Burst (ft)

Yield

(kilotons)c

EDDY LASL Sep 19 Sep 19 7 a.m. Area 7 Balloon 500 0.083

MORA LASL Sep 28 Sep 29 6:05 a.m. Area 7 Balloon 1,500 2

TAMALPAIS UCRL Oct 8 Oct 8 2 p.m. Area 12 Tunnel -407 0.072

QUAY LASL Oct 10 Oct 10 6:30 a.m. Area 7 Tower 100 0.079

LEA LASL Oct 13 Oct 13 5:20 a.m. Area 7 Balloon 1,500 1.4

HAMILTON DOD/

UCRL

Oct 15 Oct 15 8 a.m. Area 5 Tower 50 0.0012

LOGAN UCRL Oct 15 Oct 15 10 p.m. Area 12 Tunnel -932 5

DONA ANA LASL Oct 16 Oct 16 6:20 a.m. Area 7 Balloon 450 0.037

RIO ARRIBA LASL Oct 18 Oct 18 6:25 a.m. Area 3 Tower 72.5 0.09

SOCORRO LASL Oct 21 Oct 22 5:30 a.m. Area 7 Balloon 1,450 6

WRANGELL UCRL Oct 20 Oct 22 8:50 a.m. Area 5 Balloon 1,500 0.115

RUSHMORE UCRL Oct 19 Oct 22 3:40 p.m. Area 9 Balloon 500 0.188

SANFORD UCRL Oct 23 Oct 26 2:20 a.m. Area 5 Balloon 1,500 4.9

DE BACA LASL Oct 26 Oct 26 8 a.m. Area 7 Balloon 1,500 2.2

EVANS UCRL Oct 24 Oct 29 4 p.m. Area 12 Tunnel 852 0.055

MAZAMA UCRL Oct 27 Oct 29 3:20 a.m. Area 9 Tower 50 0

HUMBOLDT DOD/

UCRL

Oct 29 Oct 29 6:45 a.m. Area 3 Tower 25 0.0078

SANTA FE LASL Oct 29 Oct 30 7 p.m. Area 7 Balloon 1,500 1.3

BLANCA UCRL Oct 29 Oct 30 7 a.m. Area 12 Tunnel -987 22

a Source: United States Nuclear Tests, July 1945 through September 1992, DOE/NV-209 (Rev. 15), Dec 2000.

b Pacific Daylight Time for Shot EDDY; Pacific Standard Time for all other shots. c One kiloton equals the approximate energy release of one thousand tons of TNT.
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Summary of Operation HARDTACK II Safety Tests (1958)a

Shot Sponsor Planned

Date Actual Date Local Timeb NTS Location Type Height of Burst (ft)

Yield

(kilotons)c

OTERO LASL Sep 11 Sep 12 1 p.m. Area 3 Shaft -480 0.038

BERNALILLO LASL Sep 17 Sep 17 12:30 p.m. Area 3 Shaft -456 0.015

LUNA LASL Sep 21 Sep 21 noon Area 3 Shaft -484 0.0015

MERCURY UCRL Sep 23 Sep 23 3 p.m. Area 12 Tunnel -183 Slight

VALENCIA LASL Sep 26 Sep 26 1 p.m. Area 3 Shaft -484 0.002

MARS UCRL Sep 27 Sep 28 5 p.m. Area 12 Tunnel -140 0.013

HIDALGO LASL Oct 3 Oct 5 6:10 a.m. Area 7 Balloon 377 0.077

COLFAX LASL Oct 5 Oct 5 8:15 a.m. Area 3 Shaft -350 0.0055

NEPTUNE UCRL Oct 14 Oct 14 10 a.m. Area 12 Tunnel -110 0.115

VESTA UCRL Oct 17 Oct 17 3 p.m. Area 9 Surface 0 0.024

SAN JUAN LASL Oct 20 Oct 20 6:30 p.m. Area 3 Shaft -234 0

OBERON UCRL Oct 22 Oct 22 12:30 p.m. Area 8 Tower 25 0

CATRON LASL Oct 24 Oct 24 7 a.m. Area 3 Tower 72.5 0.021

JUNO UCRL Oct 23 Oct 24 8:01 a.m. Area 9 Surface 0 0.0017

CERES UCRL Oct 25 Oct 26 8 p.m. Area 8 Tower 25 0.0007

CHAVEZ LASL Oct 27 Oct 27 6:30 p.m. Area 3 Tower 52.5 0.0006

GANYMEDE UCRL Oct 29 Oct 30 3 a.m. Area 9 Surface 0 0

TITANIA UCRL Oct 30 Oct 30 12:34 p.m. Area 8 Tower 25 0.0002

a Source: United States Nuclear Tests, July 1945 through September 1992, DOE/NV-209 (Rev. 15), Dec 2000.

b Pacific Daylight Time for Shots OTERO through MARS; Pacific Standard Time for the remaining shots. c One kiloton equals the approximate energy release of one thousand tons of TNT.
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