American
Nuclear
Weapons
Part of the nuclear arms race
during the Cold War
Tests conducted between 1945 & 1962
Operation Hardtack I
Pacific Proving Grounds

In 1958 the arms race proceeded apace, with the enormous weapons production infrastructure and both weapons labs operating at full speed. Hardtack I included 35 tests, the largest test series so far (1958 in fact saw a total of 77 U.S. tests, more than the three previous record setting years combined). Partly this burst of testing activity was due to building pressure for an imminent test moratorium, leading the weapons labs to rush as many device types to the test range as possible. A total of 35.6 megatons were shot during this series.

The lab tests centered on ICBM and SLBM missile warheads and high yield strategic bombs. The DOD conducted high altitude multi-megaton tests to study their usefulness for ABM (anti-ballistic missile) warheads, and discovered the high-altitude EMP (electromagnetic pulse) effect in the process. Effects tests of underwater explosions were also conducted.

At least 14 mark-designated warheads were tested, plus additional developmental designs not yet awarded a serial number. These included the Mk/TX/XW - 7, 25, 31, 34, 35, 39, 41, 43, 46/53, 47, 49, 50, and 51. This series fired the largest tests since Ivy and Castle (and never equalled since in later U.S. tests) and led to the development and deployment of the largest U.S. weapon ever fielded, the 25 Mt Mk-41 bomb; and the largest U.S. missile warhead ever fielded, the W-53 9 Mt Titan-II warhead. An air dropped bomb variant of the W-53 was the largest (and oldest) weapon in the U.S. inventory up until its retirement in early 1997. The UCRL test of the W-47 Polaris warhead prototype was a major technological breakthrough that led to high yields in small light packages charcteristic of all U.S. missile warheads today.

The extensive test schedule required the use not only of both atolls (Bikini and Enewetak) but Johnston Island also. This series was the last to conduct atmospheric testing at Bikini and Enewetak atolls. Names were taken from North American trees and shrubs.

Bluegill Triple Prime, a high altitude nuclear test part of Operation Fishbowl, 26th October 1962.
High-altitude tests

Operation Hardtack I contained three high altitude tests that were designed to study many effects that a nuclear explosion would have on materials and electronic systems. They were also used to test the energy of the explosion and what forms of energy they would produce. Yucca was the name of the first high-altitude nuclear test and it was performed near the Enewetak Atoll in the Marshall Islands. The other two high-altitude tests, Orange and Teak, were performed near the Johnston Atoll in the South Pacific Ocean about 1,300 kilometers South West of the Hawaiian Islands.

Surface Blast Tests

Of the 35 nuclear tests in Operation Hardtack I, four were surface burst shots: Cactus, Koa, Quince and Fig. These tests took place from May to August 1958, all at the Enewetak Atoll. Surface tests inherently present the potential for more radioactive exposure issues than the high-altitude or underwater detonations. This is because there is more material present to be converted to radioactive debris by excess neutrons due to the proximity to the Earth’s surface, and due to the soil and other minerals excavated from the craters created by these blasts. The existence of this extra material allows for larger radioactive particles to be created and lifted into the blast cloud, falling back to the surface as fallout. Though surface and near-surface tests that have a higher probability of radioactive exposure problems, the radioactive elements have significantly shorter residence times when injected into the atmosphere. As radioactive clouds from surface-type tests reach heights of around 20 kilometers at maximum, and thus cannot extend higher than the lower stratosphere, the residence times can be up to 13 years less than the high-altitude blasts. During original concept planning in 1954, Enewetak was supposed to be the location of the smaller tests conducted during Operation Hardtack I. Due to poor weather conditions and policy changes in 1958, five of the UCRL tests which were planned to be conducted at the Bikini Atoll were moved to Enewetak. This included the later two surface blast devices in the Quince and Fig tests.

Underwater Tests

Underwater tests were conducted to assess the damages to Navy boats and materials. The location for these tests was chosen to be Enewetak. This location was chosen due to the uniformity of the bottom of the sea around Enewetak. This is critical for the tests so that proper moorings of the target ships can be secured on the sea floor. The underwater explosions create a bubble from the expended energy of the blast. This bubble is due to the vaporization of water that directly absorbs the heat of the blast. This bubble may break the surface depending on how much energy is dispersed and the depth of the nuclear device. The bubble displaces large amounts of water that then collapses in on the bubble after all the energy is expended. The water collapsing in on the cavity is called the "radioactive pool" and has the highest concentration of radioactive material.

Many different projects were put in place to test the two underwater blasts. Wave generation, hydrodynamic variables, and energy released were all studied using multiple sensors. These sensors were placed in multiple areas such as target ships and floating balloons. Oceanographic, seismographic and hydrographic surveys were completed after each nuclear blast was completed to further the data. A project that used a nuclear blast to clear minefields was studied using the Umbrella blast. 120 inert mines were placed at different distances ranging from 1,500 feet to 8,000. These mines were then picked out of the water to study the effects of the blast at each interval.

Image of the Pacific Ocean, showing especially the main U.S. government nuclear testing sites in the Pacific Proving Grounds (Marshall Islands, Bikini Atoll, Johnston Island).
Operation Hardtack I
1958
Notable tests from Operation Hardtack I

Information

Test: Orange
Time: 10:30 12 August 1958 (GMT)
Location: Johnston Island
Test Type: Rocket
Test Height: 141,000ft
Yield - Actual (Predicted): 3.8 Mt (-)

Comments:

Orange was launched twelve days after Teak on August 11, 1958. Orange, like Teak, was launched using a Redstone Missile and had a yield of 3.8 megatons. The same safety precautions used by Teak were implemented again for the Orange launch. Seeing how smoothly the evacuation for the Teak launch went it was decided that the evacuation did not need to occur the day before the launch and eight hundred and eight men were evacuated on August 11 to an aircraft carrier about 70 kilometers northeast of the island. Along with protection for the project crew, it was decided after Teak that Sand Island, a local bird refuge, would need protection from the blast as well. To make sure that most of the wildlife was safe a smoke screen was created over Sand Island. Due to interest in Hawaii, it was announced on August 11 that there would be a nuclear test sometime between 10 PM and 6 AM. The rocket carrying the warhead was launched at 11:27 from Johnston Island and traveled south. Like Teak, the flight lasted 3 minutes and was detonated at 11:30 PM about 41 kilometers south of Johnston Island at an altitude of about 43 kilometers. The trajectory of Orange was a major success after the incident with Teak being detonated directly over the island. The recovery crew for the pod that was with Orange was unable to locate the research pod which had been launched with the rocket. Although Orange was visible from Hawaii it was not as great of a spectacle as Teak had been. The light from the blast was only visible for about 5 minutes. The explosion had also been slightly obscured to the crew at Johnston Island from cloud coverage that night. The blast from Orange did not come with large communication interruption that Teak had caused, but some commercial flights to Hawaii were said to have lost contact with air traffic controllers for a short period of time.

Information

Test: Umbrella
Time: 23:15 8 June 1958 (GMT)
Location: Enewetak lagoon
Test Type: Underwater
Test Height: -150ft
Yield - Actual (Predicted): 8 kt (-)

Comments:

Umbrella was a DOD sponsored weapons effects test for a medium depth underwater explosion. A Mk-7 bomb was used for the test (30 inches in diameter, 54 inches long, device weight 825 lb.) in a heavy pressure vessel (total weight 7000 lb.). Very similar to the Wahoo device. The device was detonated on the lagoon bottom NNE of Mut (Henry) Island. An underwater crater 3000 feet across and 20 feet deep was produced.

Information

Test: Oak
Time: 19:30 28 June 1958 (GMT)
Location: Enewetak lagoon
Test Type: Barge
Test Height: 8.6ft
Yield - Actual (Predicted): 8.9 Mt (7.5 Mt)

Comments:

Prototype test of the LASL designed TX-46 system. Similar to the devices tested in Butternut (an 81 kt primary test) and Yellowwood (a fizzle). The second stage was beefed up after the Yellowwood failure, this was also a standard "dirty" configuration (in contrast to the "clean" version fired in Yellowwood). This test exceeded the predicted yield of 7.5 Mt. The fission yield was predicted to be 4 Mt, actual fission yield was 5 Mt. This is one of the largest devices ever tested by the U.S. (6th largest U.S. test). The test was conducted in very shallow water (12 feet). The device was horizontal on the barge, with the axis 3 feet above the barge deck, which was in turn 5.6 feet above the water line. The barge used for the test weighed 223 tons and was unballasted to provide a shallow draft. The subsurface crater produced was 5740 feet diameter and 204 feet deep. The test device was 37 inches in diameter and 100.5 inches long, and weighed 6113 lb. This design was later developed into the 9 Mt W/Mk-53 warhead deployed on the Titan II missile and the Mk-53 strategic bomb. This last version remained in active service until early 1997, making it the oldest and highest yield weapon in the U.S. stockpile (it is not clear whether it is still being held in the reserve stockpile, or whether it has slated for dismantlement).

Information

Test: Teak
Time: 10:50 1 August 1958 (GMT)
Location: Johnston Island
Test Type: Rocket
Test Height: 252,000ft
Yield - Actual (Predicted): 3.8 Mt (-)

Comments:

At time of detonation the rocket had flown to an altitude of 76.2 kilometers. The explosion could be seen from Hawaii 1,297 kilometers away and was said to be visible for almost half an hour. After the explosion, high frequency long distance communication was interrupted across the Pacific. Due to this communication failure Johnston Island was unable to contact their superiors in the US to let them know the results of the test until about eight hours after the detonation. Thirty minutes after detonation, a crew was sent out to collect the pod which had detached from the missile carrying the warhead. The pod had been irradiated and to handle it the crew members used disposable gloves in an attempt to protect themselves from beta radiation.

Operation Hardtack II
Nevada Test Site

1958 was a banner year for nuclear weapons testing by the U.S, with a total of 77 U.S. tests, more than the three previous record setting years combined. This burst of testing activity was partly due to building pressure for an imminent test moratorium, leading the weapons labs to rush as many device types to the test range as possible, and partly due to the accelerating momentum of the arms race of the 1950s hitting full stride. 1958 was exceeded only by the 96 tests in 1962, sandwiched as it was between a testing moratorium followed by a surprise moratorium breakout by the Soviet Union in 1961, and the imminent prospect of a permanent atmospheric testing ban.

Hardtack II included 37 tests, the largest test series so far, exceeding the 35 tests of the just completed Hardtack I. Hardtack I had focused primarily on high yield proof or developemental tests of complete thermonuclear weapons, which necessitated it be conducted in the distant Pacific (a total of 35.6 Mt being fired). In contrast, Hardtack II consisted exclusively of low yield tests, many of them attempted zero-yield one-point safety tests, which could be conducted in relative safety in Nevada (some were underground). Only 45.8 kt total was fired in Hardtack II, and of this only 18.5 kt was fired above ground. This was a dramatic turnaround from the previous Nevada test series, Plumbbob, in which the above ground Hood shot by itself was 74 kt. Concern about the effects of fallout on the U.S. was certainly making itself felt.

Most of the tests were efforts to prove the safety and effectiveness of new "sealed pit" fission primaries and tactical weapons. This task proved extremely difficult, caught between the Scylla of safety (ensuring that accidental detonation of the explosive could not create even a small nuclear yield) and the Charybdis of effectiveness (ensuring that the weapon reached its design yield). Effective designs often proved unsafe, and modifications made to achieve safety often led to fizzles. As a result, despite the large number of tests, only a fairly small number of application systems were actually under development. For example, at least 10 shots were conducted to verify the safety and effectiveness of a primary for the XW-54 warhead. No more than 7 design types account for at least 29 of the tests. This series included tests of what is probably the lightest nuclear system feasible - the XW-51 Davy Crockett warhead - weighing only 16 kg in its tested form.

Martin RB-57D-2 Model 796 53-3979 collecting atmospheric data during Juniper Nuclear bomb test; Operation Hardtack I 22 July 1958 at Bikini Atoll.
Operation Hardtack II
1958
Notable tests from Operation Hardtack II

Information

Test: De Baca
Time: 16:00 26 October 1958 (GMT)
Location: NTS, Area 7b
Test Type: Balloon
Test Height: 1,500ft
Yield - Actual (Predicted): 2.2 kt (>2.2 kt)

Comments:

Another attempt at firing a full yield version of the XW-54/Gnat system puts in a disappointing showing. Similar to the Catron and Mora devices the 2.2 kt yield was below predictions. Device dimensions: 11.3 inches in diameter, 15 inches long, weight 66 lb.

Operation Hardtack I

Country: United States
Test Site: Pacific Proving Grounds
Test Type: Multiple
Period: 1958
Number of Tests: 35
Total Yield: 9.3 Megatons of TNT (39 PJ)

Operation Hardtack II

Country: United States
Test Site: Nevada Test Site
Test Type: Multiple
Period: 1958
Number of Tests: 37
Total Yield: 22 Kilotonnes of TNT (92 TJ)



The "ton of TNT" is a unit of energy defined by that convention to be 4.184 gigajoules, which is the approximate energy released in the detonation of a metric ton (1,000 kilograms or one megagram) of TNT.
Yield

38 t
15 t
83 t
6 kt
1.5 t
72 t
0 t
0.2 t
1.3 t
55 t
2 kt
77 t
79 t
12 t
1.4 kt
115 t
5 kt
37 t
24 t
90 t
0 t
115 t
0 t
188 t
21 t
1 t
0.7 t
4.9 kt
0.6 t
2.2 kt
55 t
78 t
0 t
0 t
2 t
22 kt
1.3 kt

22 kt
The "ton of TNT" is a unit of energy defined by that convention to be 4.184 gigajoules, which is the approximate energy released in the detonation of a metric ton (1,000 kilograms or one megagram) of TNT.
Yield

1.7 kt
1.3 Mt
81 kt
37 kt
1.3 Mt
9 kt
5.9 kt
18 kt
25.1 kt
57 kt
11.6 kt
92 kt
15 kt
213 kt
330 kt
319 kt
1.45 kt
8 kt
412 kt
880 kt
8.9 Mt
14 kt
5.2 kt
220 kt
397 kt
0 t
9.3 Mt
255 kt
202 kt
65 kt
2 Mt
3.8 Mt
0 t
3.8 Mt
2 t

9.3 Mt
Code by Luke Hoban