Instruct: Given a question, retrieve relevant passages that can help answer the question.
Query: What was the last high-yield thermonuclear weapon design test conducted by the US at Bikini Atoll?
Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of Operation Castle. Detonated on March 1, 1954, the device was the most powerful nuclear device detonated by the United States and its first lithium deuteride fueled thermonuclear weapon.[1][2] Castle Bravo's yield was 15 megatons of TNT, 2.5 times the predicted 6.0 megatons, due to unforeseen additional reactions involving 7Li,[3] which led to the unexpected radioactive contamination of areas to the east of Bikini Atoll.
The seventeen-shot Redwing series followed—eleven tests at Enewetak Atoll and six at Bikini. The island residents who had been promised they would be able to return home to Bikini was thwarted indefinitely by the U.S. decision to resume nuclear testing at Bikini in 1954. During 1954, 1956, and 1958, twenty-one more nuclear bombs were detonated at Bikini, yielding a total of , equivalent to more than three thousand "Baker" bombs. Only one was an air burst, the 3.8 Mt Redwing "Cherokee" test. Air bursts distribute fallout in a large area, but surface bursts produce intense local fallout. These tests were followed by the 33-shot Hardtack tests which began in late April 1958. The last of ten tests were detonated on Bikini Atoll on 22 July 1958.
The goal of China was to produce a thermonuclear device of at least a megaton in yield that could be dropped by an aircraft or carried by a ballistic missile. Several explosions to test thermonuclear weapon designs, characteristics and yield boosting preceded the thermonuclear test.
In July 1954, the Cabinet decided to develop the hydrogen bomb. The United Kingdom Atomic Energy Authority Atomic Weapons Research Establishment at Aldermaston produced three designs: Orange Herald, a large boosted fission weapon; Green Bamboo, an interim thermonuclear design; and Green Granite, a true thermonuclear weapon. The first test series consisted of three tests in May and June 1957. In the first, Grapple 1, a version of Green Granite known as Short Granite was dropped from a Vickers Valiant bomber flown by Wing Commander Kenneth Hubbard. The bomb's yield was estimated at , far below its designed capability. Despite its failure, the test was hailed as a successful thermonuclear explosion, and the government did not confirm or deny reports that the UK had become a third thermonuclear power. The second test was Grapple 2, of Orange Herald. Its yield made it technically a megaton weapon. It was the largest ever achieved by a single stage device. Grapple 3 tested Purple Granite, a Short Granite with some fixes. Its yield was a very disappointing .
On July 19, 1956, AEC Chairman Lewis Strauss said that the Redwing Zuni shot clean bomb test "produced much of importance ... from a humanitarian aspect." However, less than two days after this announcement, the dirty version of Bassoon, called Bassoon Prime, with a uranium-238 tamper in place, was tested on a barge off the coast of Bikini Atoll as the Redwing Tewa shot. The Bassoon Prime produced a 5-megaton yield, of which 87% came from fission. Data obtained from this test, and others, culminated in the eventual deployment of the highest yielding US nuclear weapon known, and the highest yield-to-weight weapon ever made, a three-stage thermonuclear weapon with a maximum "dirty" yield of 25 megatons, designated as the B41 nuclear bomb, which was to be carried by U.S. Air Force bombers until it was decommissioned; this weapon was never fully tested.
Shipwrecks in the lagoon include:The following above-ground nuclear device tests were conducted on or near Bikini Atoll from 1946 to 1958, comprising 15.1% of total test yield worldwide. These dates are given in US Eastern time zone The days of the week are a day earlier than they were at Bikini 
North Korea claimed to have tested its miniaturised thermonuclear bomb on 6 January 2016. North Korea's first three nuclear tests (2006, 2009 and 2013) were relatively low yield and do not appear to have been of a thermonuclear weapon design. In 2013, the South Korean Defense Ministry has speculated that North Korea may be trying to develop a "hydrogen bomb" and such a device may be North Korea's next weapons test. In January 2016, North Korea claimed to have successfully tested a hydrogen bomb, though only a magnitude 5.1 seismic event was detected at the time of the test, a similar magnitude to the 2013 test of a 6-9 kt atomic bomb. These seismic recordings have scientists worldwide doubting North Korea's claim that a hydrogen bomb was tested and suggest it was a non-fusion nuclear test. On 9 September 2016, North Korea conducted their fifth nuclear test which yielded between 10 and 30 kilotons.
On March 1, 1954, the U.S. detonated its first practical thermonuclear weapon (which used isotopes of lithium as its fusion fuel), known as the "Shrimp" device of the Castle Bravo test, at Bikini Atoll, Marshall Islands. The device yielded 15 megatons, more than twice its expected yield, and became the worst radiological disaster in U.S. history. The combination of the unexpectedly large blast and poor weather conditions caused a cloud of radioactive nuclear fallout to contaminate over 7,000 square miles (18,000km2). 239 Marshall Island natives and 28 Americans were exposed to significant amounts of radiation, resulting in elevated levels of cancer and birth defects in the years to come.[29]
The nuclear weapons testing at Bikini Atoll program was a series of 23 nuclear devices detonated by the United States between 1946 and 1958 at seven test sites. The test weapons were detonated on the reef itself, on the sea, in the air and underwater with a combined fission yield of 42.2 Mt. The testing began with the Operation Crossroads series in July 1946. Shortly after World War II ended, President Harry S. Truman directed Army and Navy officials to secure a site for testing nuclear weapons on American warships. While the Army had seen the results of a land-based explosion, the Navy wanted to know the effect of a nuclear weapon on ships. They wanted to determine whether ships could be spaced at sea and in ports in a way that would make nuclear weapons ineffective against vessels.
Two test devices were fielded in 1953 as part of operation Upshot–Knothole. The principal aim of the University of California Radiation Laboratory designs was a preliminary "nucleonics investigation" for a spherical deuterated polyethylene charge containing uranium deuteride as a candidate thermonuclear fuel for the "Radiator", an early incarnation of the "Morgenstern". It was hoped that deuterium would fuse (become an active medium) in the secondary's core if compressed appropriately through radiation implosion. The fuel was selected so that UCRL's thermonuclear program would not compete with LASL's on scarce materials at the time, specifically lithium. If successful, the devices could also lead to a compact primary containing minimal amount of fissile material, and powerful enough to ignite Ramrod the other Mark 22 nuclear bomb prototype designed by UCRL at the time. For a hydride-type primary, the degree of compression would not make deuterium to fuse, thus the design would be essentially a pure fission weapon, not a boosted one. The devices themselves as tested in Upshot-Knothole were experimental systems, not weapon prototypes, and were not designed to be used as weapons, or thermonuclear primaries. The cores consisted of a mix of uranium deuteride (UD), powder-compacted with deuterated polyethylene. No boron was used. The core tested in "Ray" used uranium with low enrichment in U, and in both shots deuterium acted as the neutron moderator. The predicted yield was 1.5 to 3 kt for "Ruth" (with a maximum potential yield of 20 kt) and 0.5-1 kt for "Ray". The tests produced yields of 200 tons of TNT each; both tests were considered to be fizzles.
The Navy then selected Ujelang Atoll for their temporary home and some young men from the Bikini Atoll population went ahead to begin constructing living accommodations. But U.S. Trust Authorities changed their mind. They decided to use Enewetak Atoll as a second nuclear weapons test site and relocated that atoll's residents to Ujelang Atoll instead and to the homes built for the Bikini Islanders.
Mason requested that food be brought to the islanders on Rongerik immediately along with a medical officer. The Navy then selected Ujelang Atoll for their temporary home and some young men from the Bikini Atoll population went ahead to begin constructing living accommodations. But U.S. Trust Authorities changed their mind. They decided to use Enewetak Atoll as a second nuclear weapons test site and relocated that atoll's residents to Ujelang Atoll instead and to the homes built for the Bikini Islanders.
The French nuclear testing site was moved to the unpopulated French atolls in the Pacific Ocean. The first test conducted at these new sites was the "Canopus" test in the Fangataufa atoll in French Polynesia on 24 August 1968, the country's first multistage thermonuclear weapon test. The bomb was detonated from a balloon at a height of 520 meters. The result of this test was significant atmospheric contamination. Very little is known about France's development of the Teller–Ulam design, beyond the fact that France detonated a 2.6 Mt device in the 'Canopus" test. France reportedly had great difficulty with its initial development of the Teller-Ulam design, but it later overcame these, and is believed to have nuclear weapons equal in sophistication to the other major nuclear powers.
Operation Antler followed in 1957. Antler was designed to test components for thermonuclear weapons, with particular emphasis on triggering mechanisms. Three tests began in September, codenamed "Tadje", "Biak" and "Taranaki". The first two tests were conducted from towers, the last was suspended from balloons. Yields from the weapons were , and respectively. The Tadje test used cobalt pellets as a 'tracer' for determining yield; later rumours developed that Britain had been developing a cobalt bomb. The Royal Commission found that personnel handling these pellets were later exposed to the active cobalt 60. Although the Antler series were better planned and organised than earlier series, intermediate fallout from the Taranaki test exceeded predictions.
The United States was in a Cold War Nuclear arms race with the Soviet Union to build bigger and better bombs. The next series of tests over Bikini Atoll was code named Operation Castle. The first test of that series was Castle Bravo, a new design utilizing a dry fuel thermonuclear hydrogen bomb. It was detonated at dawn on March 1, 1954.
Much of the stimulus for the treaty was increasing public unease about radioactive fallout as a result of above-ground or underwater nuclear testing, particularly given the increasing power of nuclear devices, as well as concern about the general environmental damage caused by testing. In 1952–53, the US and Soviet Union detonated their first thermonuclear weapons (hydrogen bombs), far more powerful than the atomic bombs tested and deployed since 1945. In 1954, the US Castle Bravo test at Bikini Atoll (part of Operation Castle) had a yield of 15 megatons of TNT, more than doubling the expected yield. The Castle Bravo test resulted in the worst radiological event in US history as radioactive particles spread over more than , affected inhabited areas (including Rongelap Atoll and Utirik Atoll), and sickened Japanese fishermen aboard the "Lucky Dragon" upon whom "ashes of death" had rained. In the same year, a Soviet test sent radioactive particles over Japan. Around the same time, victims of the atomic bombing of Hiroshima visited the US for medical care, which attracted significant public attention. In 1961, the Soviet Union tested the Tsar Bomba, which had a yield of 50 megatons and remains the most powerful man-made explosion in history, though due to a highly efficient detonation fallout was relatively limited. Between 1951 and 1958, the US conducted 166 atmospheric tests, the Soviet Union conducted 82, and Britain conducted 21; only 22 underground tests were conducted in this period (all by the US).
Castle Yankee was the code name given to one of the tests in the Operation Castle series of American tests of thermonuclear bombs. It was originally intended as a test of a TX-16/EC-16 bomb, but the design became obsolete after the Castle Bravo test was successful. The test device was replaced with a TX-24/EC-24 bomb which was detonated on May 5, 1954, at Bikini Atoll.
It released energy equivalent to 13.5 megatons of TNT, the second-largest yield ever in a U.S. fusion weapon test.
Only six countries—United States, Russia, United Kingdom, China, France, and India—have conducted thermonuclear weapon tests. (Whether India has detonated a "true" multi-staged thermonuclear weapon is controversial.)[15] North Korea claims to have tested a fusion weapon as of January2016, though this claim is disputed.[16] Thermonuclear weapons are considered much more difficult to successfully design and execute than primitive fission weapons. Almost all of the nuclear weapons deployed today use the thermonuclear design because it is more efficient.
The first "Ivy" shot, "Mike", was the first successful full-scale test of a multi-megaton thermonuclear weapon ("hydrogen bomb") using the Teller-Ulam design. Unlike later thermonuclear weapons, "Mike" used deuterium as its fusion fuel, maintained as a liquid by an expensive and cumbersome cryogenic system. It was detonated on Elugelab Island yielding 10.4 megatons, almost 500 times the yield of the bomb dropped on Nagasaki. Eight megatons of the yield was from fast fission of the uranium tamper, creating massive amounts of radioactive fallout. The detonation left an underwater crater 6,240 ft (1.9 km) wide and 164 ft (50 m) deep where Elugelab Island had been. Following this successful test, the "Mike" design was weaponized as the EC-16, but it was quickly abandoned for solid-fueled designs after the success of the Castle Bravo shot.
Operation Redwing was a United States series of 17 nuclear test detonations from May to July 1956. They were conducted at Bikini and Enewetak atolls by Joint Task Force 7 (JTF7). The entire operation followed "Project 56" and preceded "Project 57". The primary intention was to test new, second-generation thermonuclear weapons. Also tested were fission devices intended to be used as primaries for thermonuclear weapons, and small tactical weapons for air defense. "Redwing" demonstrated the first United States airdrop of a deliverable hydrogen bomb during test "Cherokee". Because the yields for many tests at "Operation Castle" in 1954 were dramatically higher than predictions, "Redwing" was conducted using an "energy budget": There were limits to the total amount of energy released, and the amount of fission yield was also strictly controlled. Fission, primarily "fast" fission of the natural uranium tamper surrounding the fusion capsule, greatly increases the yield of thermonuclear devices, and constitutes the great majority of the fallout, as nuclear fusion is a relatively clean reaction.
The goal of China was to produce a thermonuclear device of at least a megaton in yield that could be dropped by an aircraft or carried by a ballistic missile. Several explosions to test thermonuclear weapon designs, characteristics and yield boosting preceded the thermonuclear test.
Seventeen nuclear weapons were detonated on the Bikini and Enewetak Atolls as part of Operation Redwing in 1956. Many of them were designed to prove the feasibility of numerous thermonuclear weapon designs, with yields ranging from around 2 to 5 Mt.
The nuclear testing at Bikini Atoll program was a series of 23 nuclear devices detonated by the United States between 1946 and 1958 at seven test sites on the reef itself, on the sea, in the air and underwater. The test weapons produced a combined fission yield of 42.2 Mt of explosive power.
On 2 January 1954, the dock landing ship sailed for Pearl Harbor in preparation for Operation Castle, a six-detonation atmospheric nuclear test slated to occur at Bikini and Eniwetok atolls in the Marshall Islands. Arriving at Bikini Atoll on 19 January, "Belle Grove" resumed the familiar role of transport and "mother" ship to a boat pool of 26 small craft. In addition, before each test, the ship evacuated people and boats from the test sites. Following each test, she quickly returned to the lagoon to enable LCM decontamination and recovery operations to proceed as soon as possible. The first five thermonuclear detonations occurred at Bikini between 1 March and 5 May, and the last one took place on 14 May at Eniwetok.
With his doctorate in hand, Agnew returned to Los Alamos as a National Research Foundation Fellow, and worked on weapons development in the Physics Division. In 1950, he was assigned to the thermonuclear weapons project, and was project engineer for the Castle Bravo nuclear test at Bikini Atoll in 1954. He became head of the Weapon Nuclear Engineering Division in 1964.