Operation Hardtack I was a series of 35 nuclear tests carried out by the United States from April 28 to August 18, 1958, at the Pacific Proving Grounds. At the time, this test series had more nuclear explosions than all previous nuclear tests in the Pacific Ocean combined. These tests happened after the Project 58/58A series, which took place from December 6, 1957, to March 14, 1958, and before the Operation Argus series, which occurred from August 27 to September 6, 1958.
Operation Hardtack I was managed by Joint Task Force 7 (JTF 7). JTF 7 included members of the U.S. military, federal civilian workers, and employees from the Department of Defense (DOD) and the Atomic Energy Commission (AEC). The group had 19,100 people working together.
There were three main research goals. First, scientists tested new types of nuclear weapons by exploding experimental devices made by the AEC's Los Alamos Scientific Laboratory and the University of California Radiation Laboratory (UCRL). The DOD also tested these explosions in ways that did not interfere with the AEC's work. Second, the DOD studied how underwater explosions affected Navy ships and other equipment. One test, called Wahoo, happened in open ocean water, while another, Umbrella, took place in a lagoon. Third, researchers studied high-altitude nuclear tests to improve methods for detecting such tests and to develop ways to defend against ballistic missiles. This research included three tests—Orange, Teak, and Yucca—which were the first high-altitude nuclear tests. Orange and Teak were part of a group called Operation Newsreel and used rockets to reach high altitudes. Yucca used balloons to reach its altitude.
Historical background
Many events and actions before Operation Hardtack I, such as results from earlier nuclear tests and the political situation around the world, influenced how it was planned and carried out. One important event was that public and international concerns about nuclear radiation were growing by 1956. During the 1956 Presidential Election, ending nuclear testing became a topic in the campaign, and nuclear safety was part of that discussion. At the same time, the Union of Soviet Socialist Republics (USSR) suggested a pause in nuclear testing.
In 1956, the National Academy of Sciences (NAS) released a report called "The Biological Effects of Atomic Radiation," which recommended new limits for how much radiation the general public could safely be exposed to. The Atomic Energy Commission (AEC), which was responsible for developing nuclear weapons, accepted these limits. Some members of the AEC believed the limits were set incorrectly and should be reviewed later. Charles L. Dunham, the AEC’s director of the Division of Biology and Medicine, said the new limits would stop testing in Nevada. Dunham and others in the AEC suggested moving future tests to the Pacific Ocean to avoid needing to study the safety of radioactive fallout.
Also in 1956, the AEC was planning a test series that included nuclear explosions that would release large amounts of nuclear fallout. This series was named Operation Plumbbob and took place from April 24 to October 7, 1957. Operation Plumbbob was followed by Project 58/58A and Operation Hardtack I. At the time, Operation Plumbbob was the largest nuclear test series held at the Nevada Test Site. President Eisenhower was careful about approving Plumbbob because of public concerns. As a result, the AEC briefly considered moving some tests from Plumbbob to the next planned Pacific test series, Operation Hardtack I, to reduce radioactive fallout near the Nevada Test Site.
When Operation Plumbbob started in the spring of 1957, planning for Operation Hardtack I was already underway, and the number of planned nuclear detonations was greater than in the Plumbbob series. At the same time, global concerns about radiation and the spread of nuclear weapons led to formal talks between the United States, USSR, and other countries about creating a worldwide ban on nuclear testing to reduce the risk of war. On August 9, 1957, AEC chairman Lewis L. Strauss proposed a plan for Operation Hardtack I to President Eisenhower. President Eisenhower objected to the four-month testing period and the plan’s request for 25 nuclear tests, which was one more than in Plumbbob. As a result, Eisenhower agreed to limit the test sizes to no more than 15 megatons of TNT (63 PJ) and ordered the testing period to be as short as possible.
Project 58/58A followed Operation Plumbbob and began in December 1957. It included four safety tests that were not meant to produce nuclear radiation. All four tests took place at the Nevada Test Site. These tests were meant to ensure bombs would not fail. However, one test called Coulomb-C malfunctioned on December 9, 1957, causing an unexpected explosion equal to 500 tons of TNT (2,100 GJ). The explosion created a cloud of radioactive fallout that traveled toward Los Angeles and caused low levels of radiation. The bomb failure increased public worry about the safety of nuclear testing.
Some tests were canceled to meet Eisenhower’s request for a shorter testing period, but new tests quickly replaced them. AEC chairman Strauss said the large number of tests was due to the "DOD’s requirement for an increasing number of different nuclear weapons types." Eisenhower eventually approved the plan for Operation Hardtack I in late January 1958, even though it still included 25 tests. On March 31, 1958, the USSR announced it would pause all tests and asked the United States to do the same. On May 9, the Soviet leader, Nikita Khrushchev, accepted Eisenhower’s invitation to discuss a nuclear testing pause, and talks began on July 1, 1958. Eisenhower announced on August 22, 1958, that the ban would start on October 31. US scientists wanted to add more tests to the Hardtack Series in case it was the last chance. As a result, Operation Hardtack I included 35 tests.
Public health concerns arose about the number of tests in Operation Hardtack I. Studies released in March 1958 showed that people as far as 400 miles (350 nmi; 640 km) away could suffer serious eye damage from two of the three high-altitude tests: Teak and Orange. Because of this, the tests were moved to Johnston Island, which was 538 miles (468 nmi; 866 km) from the nearest inhabited island. The high-altitude nuclear tests produced the first publicly reported man-made high-altitude electromagnetic pulses (EMP). Teak, which exploded at 252,000 feet (76.8 km) and had a power of 3.8 megatons of TNT (16 PJ), created a light display similar to an aurora that was visible from Hawaii, 700 nautical miles (810 mi; 1,300 km) away. Most radio communications across the Pacific Ocean stopped immediately. The blackout in Australia lasted for 9 hours, and in Hawaii, it lasted for at least 2 hours.
High-altitude tests
Operation Hardtack I included three high-altitude tests called Operation Newsreel. These tests studied how nuclear explosions might affect materials and electronic systems. They also measured the energy produced by the explosions. The first test, named Yucca, took place near Enewetak Atoll in the Marshall Islands. The other two tests, Orange and Teak, were conducted near Johnston Atoll in the South Pacific Ocean, about 1,300 kilometers (810 miles) southwest of the Hawaiian Islands.
Scientists were unsure if nuclear explosions at high altitudes could damage the ozone layer. Earlier underwater tests showed that explosions could create ozone. Project leaders believed some ozone would be destroyed but would be replaced by ozone from the explosion. They concluded that even if the theory was wrong, any damage to the ozone layer would be very small and harmless. After completing Operation Newsreel, it was found that the ozone layer was not harmed.
Yucca was the first test in Operation Hardtack I and happened on April 28, 1958. It was lifted by a balloon to an altitude of 86,000 feet (26.2 kilometers) and had a power of 1.7 kilotons of TNT (7.1 terajoules). To reach the needed height, the device was attached to a large helium-filled balloon. Launching from the ground was difficult due to strong winds on Enewetak Island, so balloons were instead launched from an aircraft carrier. This allowed the balloons to inflate in still air. Before launching, 86 balloon tests were done to ensure success.
Safety measures were used to prevent accidents. On the ground, the bomb had pins that stopped its electrical systems from working before liftoff. If the bomb failed to explode, it would detach from the balloon and fall into the ocean. Safety features on the bomb, such as probes, would detect saltwater and disable the electrical system to prevent a short circuit. If the bomb floated in the ocean after a failure, inserts would dissolve in a few hours to destroy the device.
Before the launch, weather conditions were studied to ensure the bomb would reach the correct altitude. The bomb was placed on an aircraft carrier, and testing devices were connected to the balloon. These devices sent data to ships and planes, so no recovery was needed after the explosion. After preparing the balloon, the device was released and climbed for about three and a half hours before exploding at 26.2 kilometers (16.3 miles) high. The aircraft carrier was about 4 kilometers (2.5 miles) away from the explosion site. The shock wave reached the carrier 3 minutes and 16 seconds after the explosion.
The Yucca test included research projects by the Department of Defense. Scientists studied the electromagnetic waves from the explosion to learn how they might affect electronic devices. Data from these projects was recorded on islands and planes to avoid needing to recover equipment after the test. However, five transmitting devices on the balloon could not be retrieved due to equipment problems on the aircraft carrier.
The Teak test was launched from Johnston Island on July 31, 1958, and had a power of 3.8 megatons of TNT (16 petajoules). It was the second high-altitude test after Yucca’s success. Instead of a balloon, the warhead was carried by a Redstone missile, a type of rocket used earlier in the year to launch Explorer I. Previous tests using the Redstone missile had smaller payloads, but Teak was the first high-altitude test with a megaton-level payload. The test was moved to Johnston Island to protect nearby islanders from potential eye damage caused by the explosion. The tests were named Operation Newsreel because they were relocated to Johnston Island.
Safety precautions were carefully planned. The day before the test, 187 team members left Johnston Island, and 727 people left the day of the test to minimize the number of people on the island while still allowing operations to continue. To protect against eye damage, civilian ships were kept 760 kilometers (470 miles) away from Johnston Island, and aircraft were warned not to fly within 965 kilometers (600 miles) of the island. On the day of the test, about 175 people remained on the island to prepare for the launch and handle tasks after the test.
At 11:47 PM on July 31, Teak was launched and exploded 3 minutes later at an altitude of 76.2 kilometers (47.3 miles). The explosion was visible from Hawaii, 1,297 kilometers (806 miles) away, for almost half an hour. The blast interrupted high-frequency communication across the Pacific, delaying the ability to report test results for about eight hours. Thirty minutes after the explosion, a crew collected a detached pod from the missile. The pod was radioactive, and workers used disposable gloves to protect themselves from beta radiation.
During the Teak test, all crew members on and around Johnston Island wore protective eyewear to avoid flash blindness from the explosion. After the test, scientists found that thermal radiation was also a concern, even at 76 kilometers (47 miles) high. A crew member on the island reportedly received a mild sunburn from the explosion’s heat.
Surface tests
Operation Hardtack I included 35 nuclear tests, four of which were surface bursts: Cactus, Koa, Quince, and Fig. These tests occurred between May and August 1958 at the Enewetak Atoll. Surface tests can create more radioactive exposure than high-altitude or underwater tests. This is because materials near the Earth’s surface are more likely to become radioactive debris due to neutron activity, and soil and minerals from blast craters can contribute to radioactive particles. These particles rise into the air, forming fallout that falls back to Earth. Although surface tests increase the risk of radioactive exposure, the radioactive materials stay in the atmosphere for shorter times compared to high-altitude tests. Surface test clouds typically reach about 20 kilometers (12 miles) high, staying in the lower stratosphere. This means their radioactive materials may remain in the air for up to 13 years less than high-altitude tests. Originally planned for 1954, Enewetak was chosen for smaller tests in Operation Hardtack I. However, due to weather and policy changes in 1958, five planned tests at Bikini Atoll were moved to Enewetak, including the surface tests Quince and Fig.
The Cactus test happened on May 6, 1958, at 0615. An 18-kiloton TNT (75 terajoules) explosion occurred on a platform at Runit, Enewetak. The explosion’s cloud reached 19,000 feet (5.79 km) within ten minutes and settled at 15,000 feet (4.57 km) by 20 minutes. Fallout predictions matched the actual results. Radiation levels peaked at 440 R directly above the blast site and were 1.7 R mid-island. The southern tip received only 0.005 R due to easterly winds.
DOD-affiliated Projects 1.4, 1.7, 1.8, 1.9, 1.12, 2.8, 3.2, 5.2, 5.3, 6.4, 6.5, and 6.6 involved the Cactus test. One goal was to study the crater and surrounding area before and after the blast (Project 1.4). A camera on an RB-50 aircraft mapped the crater using photogrammetry. Measurements were taken from 500 feet (152 m) to ground zero before and after the test. Radiation levels had to drop to safe levels before surveying could begin. Airblast measurements (Project 1.7) and ground pressure studies (Projects 1.8 and 1.9) also took place. Project 1.12 studied shock waves using gauges placed 625 to 965 feet (191 to 294 m) from the blast. Fallout samples were collected by aircraft (Project 2.8) to study radionuclides. A new rocket sampler, the UCRL, collected samples shortly after the test, followed by B-57D and WB-50 aircraft. Between four and 24 hours post-test, WB-50 aircraft collected samples at 1,000 feet (300 m). Project 3.2 tested corrugated steel arches placed 980 feet (300 m) from the blast. After eight days, a team removed the arch, which had radiation levels up to 0.420 R/hr. Project 5.2 studied the effects of the blast on two A4D-1 aircraft, measuring radiation with film badges. The pilot’s dosimeter showed 0.105 rem, while other badges recorded 0.49 R to 1.74 R. Project 5.3 focused on two FJ-4 aircraft, with radiation levels ranging from 0.52 R to 5.06 R. Project 6.4 studied electromagnetic pulses using instruments at Wotho and Kusaie. Project 6.6 measured the stabilized radioactive cloud after the blast.
The Koa test occurred on May 13, 1958, at 06:30 on the western side of Dridrilbwij. The blast was 1.37 megatons of TNT (5.7 petajoules), about 76 times larger than the Cactus test. Conducted in a water tank, the cloud reached 60,000 feet (18 km) within 17 minutes. Fallout predictions for Koa were larger and covered a broader area than Cactus, with radiation levels up to ten times higher near the blast. A previous test, the Apache (1.85 megatons of TNT), had damaged the island in 1956, but Koa completely destroyed it.
The DOD sponsored experiments for Koa, including Projects 1.4, 1.7, 1.8, 1.9, 1.12, 2.9, 3.2, 3.6, 5.1, 5.3, 6.4, 6.5, 6.6, 6.9, and 6.11. Project 1.4 measured land craters, with surveys starting four days after the blast due to radiation. A boat mapped the crater, though some measurements were delayed until 1959. Project 1.9 studied soil pressure by burying 43 drums 0 to 20 feet (0 to 6.1 m) deep, 3,000 feet (910 m) from the blast. Fallout samples were not collected after Koa due to technical issues, but high- and low-altitude measurements were taken without problems.
Barge tests
Barge-mounted test detonations were first used in 1954 to help with the lack of land at the HP. When testing returned to Bikini Atoll, barges were used as the shot point. One advantage was that no radioactive surface zero areas were created. Two large underwater craters formed in 1954 and were later used as surface zeros for detonations from barges. This allowed land to be used for placing measurement equipment and reusing the same burst point without long delays for radiological cooling or expensive decontamination. Reusing zero points also helped reuse instrument locations and shelters for multiple tests, saving costs and time while increasing scheduling flexibility. In HARDTACK, 26 barge events used only five detonation areas.
FIR predicted fallout, surface radiological exclusion (radex) areas, ship positions, and aircraft participation. FIR was the first Bikini detonation of the Hardtack series. It was detonated at 0550 on May 12, 1958, on a barge in the Bravo crater, producing a yield range of 1.36 megatons of TNT (5.7 PJ). After detonation, the cloud rose to 60,000 to 90,000 feet (18.3–27.4 km). The FIR detonation was followed by the BUTTERNUT detonation on Enewetak 25 minutes later. DOD-sponsored experiments for FIR included Projects 3.7, 5.1, 6.4, 6.5, 6.6, and 6.11.
BUTTERNUT predicted fallout, surface radex areas, ship positions, and aircraft participation. It was detonated at 0615 on May 12, 1958, 25 minutes after FIR at Enewetak. BUTTERNUT was detonated on a barge 4,000 feet (1.22 km) west of Runit, producing a yield range of 81 kilotons of TNT (340 TJ). The cloud rose to 35,000 feet (11 km) and stabilized at 30,000 feet (9.1 km). DOD-sponsored experiments for BUTTERNUT were Projects 5.1, 5.2, 5.3, 6.5, 6.6, and 6.9.
HOLLY predicted fallout, surface radex areas, ship positions, and aircraft participation. It was detonated at 0630 on May 21, 1958, on a barge west of Runit, 4,000 feet (1.22 km) from the nearest edge of the island, producing a yield range of 5.9 kilotons of TNT (25 TJ). The detonation produced a 15,000-foot (4.6 km) cloud that stabilized at 12,000 feet (3.7 km) at the top and 7,500 feet (2.3 km) at the base. Project 6.6 was the only DOD-sponsored experiment for HOLLY, conducted on Enewetak Island.
NUTMEG predicted fallout, surface radex areas, ship positions, and aircraft participation. The second Bikini shot, NUTMEG, was detonated at 0920 on May 22, 1958, on a barge in the ZUNI crater, producing a yield range of 25.1 kilotons of TNT (105 TJ). The detonation cloud stabilized at 20,000 feet (6.1 km) by 0926. DOD-sponsored experiments for NUTMEG were Projects 6.3, 6.3a, 6.4, 6.5, 6.6, and 6.11. Projects 6.3 and 6.3a had stations near the burst point on Eneman Island.
YELLOWWOOD predicted fallout, surface radex areas, ship positions, and aircraft participation. It was detonated at 1400 on May 26, 1958, on a barge 5,000 feet (1.5 km) southwest of Enjebi, producing a yield range of 330 kilotons of TNT (1,400 TJ). The DOD sponsored 13 experiments for YELLOWWOOD: Projects 2.4, 2.8, 3.7, 5.1, 5.2, 5.3, 6.4, 6.5, 6.6, 6.8, 6.9, 6.11, and 8.1.
MAGNOLIA predicted fallout, surface radex areas, ship positions, and aircraft participation. It was detonated at 0630 on May 28, 1958, on a barge 5,000 feet (1.5 km) west of Runit, producing a yield range of 2.1 megatons of TNT (8.8 PJ). The detonation cloud reached 50,000 feet (15.2 km) and stabilized at 35,000 feet (10.7 km). DOD-sponsored experiments for MAGNOLIA included Projects 2.4, 2.8, 3.7, 5.1, 5.2, 5.3, 6.6, 6.8, 6.9, and 8.1.
PINE predicted fallout, surface radex areas, ship positions, and aircraft participation. It was detonated at 0630 on June 1, 1958, on a barge 4,000 feet (1.22 km) west of Runit, producing a yield range of 1.3 megatons of TNT (5.4 PJ). The detonation cloud reached 50,000 feet (15.2 km) and stabilized at 30,000 feet (9.1 km). DOD-sponsored experiments for PINE included Projects 2.4, 2.8, 3.7, 5.1, 5.2, 5.3, 6.6, 6.8, 6.9, and 8.1.
MAPLE predicted fallout, surface radex areas, ship positions, and aircraft participation. It was detonated at 0630 on June 4, 1958, on a barge 5,000 feet (1.5 km) west of Runit, producing a yield range of 1.1 megatons of TNT (4.6 PJ). The detonation cloud reached 45,000 feet (13.7 km) and stabilized at 25,000 feet (7.6 km). DOD-sponsored experiments for MAPLE included Projects 2.4, 2.8, 3.7, 5.1, 5.2, 5.3, 6.6, 6.8, 6.9, and 8.
Underwater tests
Underwater tests were conducted to check for damage to Navy ships and materials. These tests took place at Enewetak because the ocean floor there is very flat, which helps secure the ships properly during testing. Underwater explosions create a bubble from the energy of the blast. This bubble forms when water turns into steam, absorbing the heat from the explosion. If the explosion has enough energy or is shallow, the bubble may reach the ocean surface. After the energy is used up, the bubble collapses, pushing water inward. This collapsing water is called the "radioactive pool" and contains the most radioactive material.
Many projects studied the effects of underwater nuclear explosions. Scientists measured wave movement, water energy, and how much energy was released using sensors placed on ships and floating balloons. After each test, ocean surveys, seismic readings, and water studies were done. One project used a nuclear blast to clear minefields. One hundred twenty inactive mines were placed at different distances, from 1,500 to 8,000 feet. These mines were later removed to study the blast's effects.
Another reason for underwater tests was to check for radiation on ships after an underwater nuclear explosion. Contaminated ships needed special "radsafe" steps so data could be recorded quickly. After recording damage and radiation levels, decontamination work was needed before repairs. A team of 200 enlisted personnel and one officer was created to clean the ships. After cleaning, the ships were repaired for future tests. Radiation exposure levels were debated for crew safety. Roentgens (1 R = about 0.01 Gy in soft tissue) were used to measure gamma radiation affecting workers.
For the underwater test crew, a limit of 5 R per blast and 10 R per operation was set. These limits were later changed to stricter maximum permissible exposure standards (MPE) by commanders. Because ships recovered quickly, high contamination levels were expected, leading to a standard of 4 R/hr. Areas with more than 4 R/hr were off-limits for recovery work. Workers in areas with more than 1 R/hr used special breathing equipment. Many workers were used to keep individual exposure below 2 R. A floating decontamination facility was built on a transport ship for the Wahoo and Umbrella tests, improving data analysis and recovery speed.
The nuclear test named Wahoo was the first underwater test in the Operation Hardtack series. It followed the Wigwam test, which was a deep-water nuclear test near San Diego. Like Wigwam, Wahoo studied the effects of underwater explosions on Navy systems. The nuclear device was placed 500 feet deep in the Pacific Ocean. Precise equipment was needed to track the test, but strong winds, currents, and tides made positioning difficult. Testing equipment was placed at depths of 400 to 800 fathoms (2,400 to 4,800 feet) around the device. The target ships included three destroyers, a submarine, a submarine model, and a merchant ship. Scientists predicted no air blast or thermal effects, and fallout would stay within the target area due to wind direction.
The test happened on May 16. Within a second, a spray dome formed, reaching 840 feet high after seven seconds. The dome looked like a cone with sloped sides. Plumes spread outward after six seconds. The vertical plume rose for 12 seconds, while side plumes lasted 20 seconds. The dome was 3,800 feet wide at 20 seconds. A base surge spread 8,000 feet downwind, helped by a 15-knot wind. The surge moved at 21 knots and was visible for 3.5 minutes. After the dome and surge faded, a foam patch spread over 6,000 feet. The blast was 9 kilotons of TNT. Fallout stayed within the predicted area, with a maximum of 0.030 R/hr. The ship 5,900 yards away was hit by the shockwave, shaking violently. The Moran ship, 2,346 feet away, was immobilized due to damage. A water sample taken one hour and ten minutes later showed 5 R/hr. The retrieval team entered an area with 3.8 R/hr after an hour and thirty-five minutes.
The second test in the Hardtack series was called Umbrella. It took place in Enewetak's lagoon, continuing the Baker test in Bikini Lagoon. Shallow water explosions can create craters if close to the ocean floor. Ships from the Wahoo test were moved to the lagoon for Umbrella. Only the Moran ship needed extra repairs. Mooring for Umbrella was easier due to the lagoon's depth. Data from Wahoo influenced Umbrella's plans for equipment placement and cleanup times. The device was placed 150 feet deep with a buoy.
The Umbrella test occurred on June 9 at 11:15 AM with clear skies and winds from the east-northeast. Within a tenth of a second, the spray dome broke the surface. The dome looked like a vertical column, with plumes shaping it. Within 20 seconds, the spray dome reached its highest point.