Download coordinates as: Operation Hardtack I was a series of 35 nuclear tests conducted by the United States from April 28 to August 18 in 1958 at the Pacific Proving Grounds.

Its 19,100 personnel were composed of members of the US military, federal civilian employees, as well as workers affiliated with the Department of Defense (DOD) and the Atomic Energy Commission (AEC).

[1][2]: 187 [3]: 3 Many events and proceedings leading up to Operation Hardtack I, such as previous nuclear testing results and the global political atmosphere, influenced its creation and design.

Charles L. Dunham, AEC Director of the Division of Biology and Medicine (DBM), said that the new limits of nuclear radiation exposure would prevent them from continuing testing in Nevada.

Dunham, in association with other AEC offices and officials, made recommendations to move further tests to the Pacific to eliminate the need to determine radiological fallout safety.

On May 9 the leader of the Soviet Union, Nikita Khrushchev, accepted Eisenhower's invitation for technical discussions on a nuclear testing moratorium and negotiations began on July 1 of the same year.

[4]: 23  Studies released in March 1958 indicated that people as far as 400 miles (350 nmi; 640 km) away could have severe retinal burns from two of the three high-altitude tests: Teak and Orange.

The other two high-altitude tests, Orange and Teak, were performed near the Johnston Atoll in the South Pacific Ocean about 1,300 kilometres (810 mi; 700 nmi) southwest of the Hawaiian Islands.

Due to issues with high winds on Enewetak Island, the balloon launches from ground were unsatisfactory, thus creating the need for a new method.

Some of these features included probes which could detect saltwater which would destroy the electrical system so the conductive seawater could not cause a short which would detonate the bomb.

Alongside testing the use of a balloon carrier, the Department of Defense wanted to research the electromagnetic waves emitted from a nuclear explosion.

[4]: 256–257  Other nuclear weapons had been tested using the Redstone missile, but until this time the highest payload to have been detonated was 3 kilotons of TNT (13 TJ) during Operation Teapot.

Due to this communication failure Johnston Island was unable to contact their superiors to advise of the test results until about eight hours after the detonation.

Unsure if this was caused by blindness or thermal radiation, the project members decided to take precautions to protect local wildlife during the Orange test.

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.

As radioactive clouds from surface-type tests reach heights of around 20 kilometers (12 mi) 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.

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.

An 18 kilotons of TNT (75 TJ) land-surface type shot was detonated on a platform at the northern tip of Runit, Enewetak in the second of the 35 tests for Operation Hardtack I.

Individuals from the Air Force Ballistic Missile Division—TRW Space Technologies Laboratory sought to the Shock Spectra Studies of Project 1.12.

[4]: 149–187  Project 1.4, which sought to study land craters post detonation for several shots, took ground survey measurements from surface zero out to 2,500 feet (760 m).

Even with these precautions, the measured alpha activity was around 20,000 counts per minute (CPM), and the area closest to surface zero was roped off to prevent personnel from entering.

[clarification needed] When testing returned to Bikini atoll the use of barges as the shot point had begun, with one notable advantage, no radioactive surface zero areas were developed.

HOLLY 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 5.9 kilotons of TNT (25 TJ) yield range.

Roentgens (1 R = ca 0,01 Gy in soft tissue) were used to gauge the gamma radiation that affected the units working on the nuclear tests.

These initial limits were rejected and maximum permissible exposure standards (MPE) were solidified by commanders for the crews working on the decontamination unit.

Due to the fast recovery of ships, high contamination values were expected by commanders and set the standard to four roentgens per hour (R/hr).

The deep water mooring systems needed for the test proved to be difficult to position, leading many analysts to believe the data skewed.

Information gathered from the Wahoo shot directly affected the Umbrella plans with regard to target array placement and decontamination times.

Some of the key points found were that underwater nuclear blasts create less fallout due to the absorption of radioactive material in the water and vaporized droplets.

The preliminary tests of explosive tapered charges were proven to simulate the shock waves of a nuclear device according to the data gathered.