Operation Castle
Encyclopedia
Operation Castle was a United States series of high-energy (high-yield
) nuclear tests by Joint Task Force SEVEN (JTF-7) at Bikini Atoll
beginning in March 1954. It followed Operation Upshot-Knothole
and preceded Operation Teapot
.
Conducted as a joint venture between the Atomic Energy Commission
(AEC) and the Department of Defense
(DoD), the ultimate objective of the operation was to test designs for an aircraft-deliverable thermonuclear weapon.
Operation Castle was considered by government officials to be a success as it proved the feasibility of deployable "dry fuel" designs for thermonuclear weapons. There were technical difficulties with some of the tests: one device had a yield much lower than its predicted yield (a "fizzle
"), while two other devices detonated with over twice their predicted yields. One test in particular, Castle Bravo
, resulted in extensive radiological contamination of nearby islands (including inhabitants and U.S. soldiers stationed there), as well as a nearby Japanese fishing boat (Daigo Fukuryū Maru
), resulting in one direct fatality and continued health problems for many of those exposed. Public reaction to the tests and an awareness of the long-range effects of nuclear fallout
has been attributed as being part of the motivation for the Partial Test Ban Treaty
of 1963.
Bikini Atoll
had previously hosted nuclear testing in 1946 as part of Operation Crossroads
where the world’s fourth and fifth atomic weapons were detonated in Bikini Lagoon. Since then, US nuclear weapons testing had moved to Eniwetok Atoll
to take advantage of generally larger islands and deeper water. Both Atolls were part of the US Pacific Proving Grounds
.
The extremely high yields of the Castle weapons caused concern within the AEC that potential damage to the limited infrastructure already established at Eniwetok would delay other operations. Additionally, the cratering from the Castle weapons was expected to be comparable to that of Ivy Mike
, a 10.4 megaton
device tested at Eniwetok in 1952 leaving a crater approximately 1 mile (1.6 km) in diameter marking the location of the obliterated test island Elugelab
.
The Ivy 'Mike' test was the world's first "hydrogen bomb", producing a full-scale thermonuclear or fusion
explosion. The 'Mike' device used liquid deuterium
, an isotope
of hydrogen
, making it a "wet bomb." The complex dewar
mechanisms needed to store the liquid deuterium at cryogenic temperatures made the device three stories tall and 82 tons in total weight, far from being a deliverable weapon. With the success of Ivy 'Mike' as proof of the Teller-Ulam bomb concept, research began on using a “dry" fuel to make a practical fusion weapon so that the United States could begin production and deployment of thermonuclear weapons in quantity. The final result incorporated lithium deuteride as the fusion fuel in the Teller-Ulam design, vastly reducing size and weight and simplifying the overall design. Operation Castle was charted to test four dry fuel designs, two wet bombs, and one smaller device. Approval for Operation Castle was communicated to JTF-7 by Major General Kenneth D. Nichols, General Manager of the AEC, on 21 January 1954.
Operation Castle was intended to test lithium deuteride (LiD) as a thermonuclear fusion fuel. A solid at room temperature, "dry" LiD, if it worked, would be far more practical than the cryogenic liquid deuterium fuel in the Ivy Mike device. The same Teller-Ulam principle would be used as in the Ivy Mike "Sausage" device, but the fusion reactions were different. Mike fused deuterium with deuterium, but the LiD devices would fuse deuterium with tritium. The tritium was produced during the explosion by irradiating the lithium with fast
neutrons.
Bravo and Union used lithium enriched in the Li-6 isotope while Romeo and Koon were fueled with natural lithium (92% Li-7, 7.5% Li-6). The use of natural lithium would be important to the ability of the US to rapidly expand its nuclear stockpile during the Cold War
arms race
.
As a hedge, development of liquid deuterium weapons continued in parallel. Even though they were much less practical because of the logistical problems dealing with the transport, handling, and storage of a cryogenic device, the cold war arms race drove the demand for a viable fusion weapon. The Ramrod and Jughead devices were liquid fuel designs greatly reduced in size and weight from their Ivy Mike "Sausage" predecessor. The Jughead device was ultimately weaponized and saw limited fielding in the inventory until the dry fuel weapons were common.
Nectar was not a fusion weapon in the same sense as the rest of the Castle series. Even though it used a dry lithium fuel for fission boosting
, the principal reaction material in the second stage was uranium and plutonium. Similar to the Teller-Ulam configuration, a fission
device was used to create high temperatures and pressures in order to compress a second fissionable mass that would have otherwise been too large to sustain an efficient reaction if it were triggered with conventional explosives. This experiment was intended to develop intermediate yield weapons for expanding the inventory (around 1-2 Mt
vs. 4-8).
Many "fusion" or "thermonuclear" weapons generate much, or even most, of their yields from fission. Although the U-238 isotope of uranium will not sustain a chain reaction, it still fissions when irradiated by the intense fast neutron flux of a fusion explosion. Because U-238 is plentiful and has no critical mass, it can be added in almost unlimited quantities as a "tamper" around a fusion bomb, helping to contain the fusion reaction and contributing its own fission energy. Fission of the U-238 tamper contributed 77% (8 megatons) to the yield of the 10.4 Mt Ivy Mike explosion.
' test. The dry fuel for 'Bravo' was 40% Li-6 and 60% Li-7. Only the Li-6 was expected to breed tritium for the deuterium-tritium fusion reaction; the Li-7 was expected to be inert. Yet J. Carson Mark
, head of the Los Alamos Theoretical Design Division, had speculated that 'Bravo' could "go big", estimating that the device could produce an explosive yield as much as 20% more than had been originally calculated. Consequently, the Li-7 component turned out to be an excellent source of tritium through a previously unquantified reaction. In actuality, 'Bravo' exceeded expectations by 250%, yielding
15 Mt
-- 1,000 times more powerful than the Little Boy
weapon used on Hiroshima
. Castle 'Bravo' remains to this day the largest atmospheric detonation ever conducted by the United States, and the seventh largest ever detonated in the world.
Because Castle 'Bravo' greatly exceeded its expected yield, JTF-7 was caught unprepared. Much of the permanent infrastructure on Bikini Atoll
was heavily damaged. The intense thermal flash ignited a fire at a distance of 20 nautical miles (37 km) on the island of Eneu (base island of Bikini Atoll). The ensuing fallout
contaminated all of the atoll, so much so, that it could not be approached by JTF-7 for 24 hours after the test, and even then exposure times were limited. As the fallout spread downwind to the east, more atolls were contaminated by radioactive calcium ash from the incinerated underwater coral banks. Although the atolls were evacuated soon after the test, 239 Marshallese on the Utirik
, Rongelap
, and Ailinginae Atoll
s were subjected to significant levels of radiation. 28 Americans stationed on the Rongerik Atoll were also exposed. Follow-up studies of the contaminated individuals began soon after the blast as Project 4.1
, and though the short-term effects of the radiation exposure for most of the Marshallese were mild and/or hard to correlate, the long-term effects were pronounced. Additionally, 23 Japanese fishermen aboard Lucky Dragon No. 5
were also exposed to high levels of radiation. They suffered symptoms of radiation poisoning
, and one crew member died in September 1954.
The heavy contamination and extensive damage from 'Bravo' significantly delayed the rest of the series. The post-'Bravo' schedule was revised on 14 April 1954.
The 'Romeo' and 'Koon' tests were complete by the time of this revision. The 'Echo' test was canceled due to the liquid fuel design becoming obsolete with the success of dry-fueled 'Bravo'. 'Yankee' was similarly considered obsolete and so was conducted using a Runt II device (similar to the 'Union' device) hastily completed at Los Alamos and flown to Bikini. With this revision, both of the "wet" fuel devices were removed from the test schedule.
As Operation Castle continued, the increased yields and fallout caused test locations to be re-evaluated. While the majority of the tests were planned for barges near the sand spit of Iroij, some were moved to the 'Bravo' and 'Union' craters. Additionally, Castle 'Nectar' was moved from Bikini Atoll to the Ivy 'Mike' crater at Eniwetok for expediency since Bikini was still heavily contaminated from the previous tests.
The final test in Operation Castle took place on 14 May 1954.
gravity bomb. The Mk-21 design project began on 26 March 1954 (just three weeks after Bravo) with production of 275 weapons beginning in late 1955. Romeo, relying on natural lithium, was rapidly turned into the Mk-17 bomb
, the US first deployable H bomb, and was available to strategic forces as an Emergency Capability by mid-1954. Most of the Castle dry fuel devices eventually appeared in the inventory and ultimately grandfathered the majority of thermonuclear configurations.
In contrast, the Livermore
-designed Koon design was a failure. Using natural lithium and a heavily modified Teller-Ulam configuration, the test produced only 110 Kt of an expected 1.5 Mt
. While engineers at the Radiation Laboratory had hoped it would lead to a promising new field of weapons, it was eventually determined that the design allowed premature heating of the lithium fuel, thereby disrupting the delicate fusion conditions.
Nuclear weapon yield
The explosive yield of a nuclear weapon is the amount of energy discharged when a nuclear weapon is detonated, expressed usually in the equivalent mass of trinitrotoluene , either in kilotons or megatons , but sometimes also in terajoules...
) nuclear tests by Joint Task Force SEVEN (JTF-7) at Bikini Atoll
Bikini Atoll
Bikini Atoll is an atoll, listed as a World Heritage Site, in the Micronesian Islands of the Pacific Ocean, part of Republic of the Marshall Islands....
beginning in March 1954. It followed Operation Upshot-Knothole
Operation Upshot-Knothole
Operation Upshot-Knothole was a series of eleven nuclear test shots conducted in 1953 at the Nevada Test Site.Over twenty-one thousand soldiers took part in the ground exercise Desert Rock V in conjunction with the Grable shot...
and preceded Operation Teapot
Operation Teapot
Operation Teapot was a series of fourteen nuclear test explosions conducted at the Nevada Test Site in the first half of 1955.During shot "Wasp", ground forces took part in Exercise Desert Rock VI which included an armored task force "Razor" moving to within 900 meters of ground zero, under the...
.
Conducted as a joint venture between the Atomic Energy Commission
United States Atomic Energy Commission
The United States Atomic Energy Commission was an agency of the United States government established after World War II by Congress to foster and control the peace time development of atomic science and technology. President Harry S...
(AEC) and the Department of Defense
United States Department of Defense
The United States Department of Defense is the U.S...
(DoD), the ultimate objective of the operation was to test designs for an aircraft-deliverable thermonuclear weapon.
Operation Castle was considered by government officials to be a success as it proved the feasibility of deployable "dry fuel" designs for thermonuclear weapons. There were technical difficulties with some of the tests: one device had a yield much lower than its predicted yield (a "fizzle
Fizzle (nuclear test)
In nuclear weapons, a fizzle occurs when the testing of a nuclear bomb fails to meet its expected yield. The reason for the failure can be linked to improper bomb design, poor construction, or lack of expertise. All countries that have had a nuclear weapons testing program have experienced fizzles...
"), while two other devices detonated with over twice their predicted yields. One test in particular, Castle Bravo
Castle Bravo
Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States ,...
, resulted in extensive radiological contamination of nearby islands (including inhabitants and U.S. soldiers stationed there), as well as a nearby Japanese fishing boat (Daigo Fukuryū Maru
Daigo Fukuryu Maru
was a Japanese tuna fishing boat, which was exposed to and contaminated by nuclear fallout from the United States' Castle Bravo thermonuclear device test on Bikini Atoll, on 1 March 1954....
), resulting in one direct fatality and continued health problems for many of those exposed. Public reaction to the tests and an awareness of the long-range effects of nuclear fallout
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
has been attributed as being part of the motivation for the Partial Test Ban Treaty
Partial Test Ban Treaty
The treaty banning nuclear weapon tests in the atmosphere, in outer space and under water, often abbreviated as the Partial Test Ban Treaty , Limited Test Ban Treaty , or Nuclear Test Ban Treaty is a treaty prohibiting all test detonations of nuclear weapons...
of 1963.
Background
Bikini Atoll
Bikini Atoll is an atoll, listed as a World Heritage Site, in the Micronesian Islands of the Pacific Ocean, part of Republic of the Marshall Islands....
had previously hosted nuclear testing in 1946 as part of Operation Crossroads
Operation Crossroads
Operation Crossroads was a series of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. It was the first test of a nuclear weapon after the Trinity nuclear test in July 1945...
where the world’s fourth and fifth atomic weapons were detonated in Bikini Lagoon. Since then, US nuclear weapons testing had moved to Eniwetok Atoll
Enewetak
Enewetak Atoll is a large coral atoll of 40 islands in the Pacific Ocean, and forms a legislative district of the Ralik Chain of the Marshall Islands. Its land area totals less than , surrounding a deep central lagoon, in circumference...
to take advantage of generally larger islands and deeper water. Both Atolls were part of the US Pacific Proving Grounds
Pacific Proving Grounds
The Pacific Proving Grounds was the name used to describe a number of sites in the Marshall Islands and a few other sites in the Pacific Ocean, used by the United States to conduct nuclear testing at various times between 1946 and 1962...
.
The extremely high yields of the Castle weapons caused concern within the AEC that potential damage to the limited infrastructure already established at Eniwetok would delay other operations. Additionally, the cratering from the Castle weapons was expected to be comparable to that of Ivy Mike
Ivy Mike
Ivy Mike was the codename given to the first United States test of a thermonuclear weapon, in which a major part of the explosive yield came from nuclear fusion. It was detonated on November 1, 1952 by the United States at on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy...
, a 10.4 megaton
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...
device tested at Eniwetok in 1952 leaving a crater approximately 1 mile (1.6 km) in diameter marking the location of the obliterated test island Elugelab
Elugelab
Elugelab was an island, part of the Enewetak atoll in the Marshall Islands. It was destroyed by the world's first test of a hydrogen bomb on 1 November 1952, as part of Operation Ivy...
.
The Ivy 'Mike' test was the world's first "hydrogen bomb", producing a full-scale thermonuclear or fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
explosion. The 'Mike' device used liquid deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...
, an isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, making it a "wet bomb." The complex dewar
Dewar flask
A Dewar flask is a vessel designed to provide very good thermal insulation. For instance, when filled with a hot liquid, the vessel will not allow the heat to easily escape, and the liquid will stay hot for far longer than in a typical container...
mechanisms needed to store the liquid deuterium at cryogenic temperatures made the device three stories tall and 82 tons in total weight, far from being a deliverable weapon. With the success of Ivy 'Mike' as proof of the Teller-Ulam bomb concept, research began on using a “dry" fuel to make a practical fusion weapon so that the United States could begin production and deployment of thermonuclear weapons in quantity. The final result incorporated lithium deuteride as the fusion fuel in the Teller-Ulam design, vastly reducing size and weight and simplifying the overall design. Operation Castle was charted to test four dry fuel designs, two wet bombs, and one smaller device. Approval for Operation Castle was communicated to JTF-7 by Major General Kenneth D. Nichols, General Manager of the AEC, on 21 January 1954.
Experiments
Operation Castle was organized into seven experiments, all but one of which were to take place at Bikini Atoll. Below is the original test schedule (as of February 1954).| Experiment | Device | Prototype | Fuel | Date | Predicted yield | Manufacturer | Test location |
|---|---|---|---|---|---|---|---|
| BRAVO Castle Bravo Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States ,... |
Shrimp | TX-21 | 40% Li-6 D (dry) | 1 March 1954 | 6 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Los Alamos Scientific Laboratory | Reef off Nam Is, Bikini |
| UNION Castle Union Castle Union was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-14 thermonuclear weapon , one of the first deployed U.S... |
Alarm Clock | EC-14 | 95% Li-6 D (dry) | 11 March 1954 | 3-4 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Los Alamos Scientific Laboratory | Barge off Iroij, Bikini |
| YANKEE Castle Yankee Castle Yankee was the code name given to one of the tests in the Operation Castle series of American tests of thermonuclear bombs.-Jughead:... |
Jughead / Runt-II | TX/EC-16 / TX/EC-24 | Cryo H-2 (wet) / 40% Li-6 D (dry) | 22 March 1954 | 8 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Los Alamos Scientific Laboratory | Barge off Iroij, Bikini |
| ECHO | Ramrod | N/A | Cryo H-2 (wet) | 29 March 1954 | 65-275 Kt | University of California Radiation Laboratory (Livermore) | Eleleron, Enewetak |
| NECTAR | Zombie | TX-15 | Boosted fission | 5 April 1954 | 1.8 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Los Alamos Scientific Laboratory | Barge off Iroij, Bikini |
| ROMEO Castle Romeo Castle Romeo was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-17 thermonuclear weapon , the first deployed U.S... |
Runt | TX/EC-17A | 7.5% Li-6 D (natural) | 15 April 1954 | 4 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Los Alamos Scientific Laboratory | Barge off Iroij, Bikini |
| KOON Castle Koon The Koon shot of Operation Castle was a test of a University of California Radiation Laboratory designed thermonuclear device.The 'dry' two-stage device was known as "Morgenstern". It was tested on 7 April 1954. The predicted yield of Morgenstern, which had a highly innovative secondary stage, was... |
Morgenstern | N/A | 7.6% Li-6 D (natural) | 22 April 1954 | 1 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
University of California Radiation Laboratory (Livermore) | Eneman, Bikini |
Operation Castle was intended to test lithium deuteride (LiD) as a thermonuclear fusion fuel. A solid at room temperature, "dry" LiD, if it worked, would be far more practical than the cryogenic liquid deuterium fuel in the Ivy Mike device. The same Teller-Ulam principle would be used as in the Ivy Mike "Sausage" device, but the fusion reactions were different. Mike fused deuterium with deuterium, but the LiD devices would fuse deuterium with tritium. The tritium was produced during the explosion by irradiating the lithium with fast
Neutron temperature
The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term temperature is used, since hot, thermal and cold neutrons are moderated in a medium with a certain temperature. The neutron energy distribution is...
neutrons.
Bravo and Union used lithium enriched in the Li-6 isotope while Romeo and Koon were fueled with natural lithium (92% Li-7, 7.5% Li-6). The use of natural lithium would be important to the ability of the US to rapidly expand its nuclear stockpile during the Cold War
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
arms race
Nuclear arms race
The nuclear arms race was a competition for supremacy in nuclear warfare between the United States, the Soviet Union, and their respective allies during the Cold War...
.
As a hedge, development of liquid deuterium weapons continued in parallel. Even though they were much less practical because of the logistical problems dealing with the transport, handling, and storage of a cryogenic device, the cold war arms race drove the demand for a viable fusion weapon. The Ramrod and Jughead devices were liquid fuel designs greatly reduced in size and weight from their Ivy Mike "Sausage" predecessor. The Jughead device was ultimately weaponized and saw limited fielding in the inventory until the dry fuel weapons were common.
Nectar was not a fusion weapon in the same sense as the rest of the Castle series. Even though it used a dry lithium fuel for fission boosting
Boosted fission weapon
A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released in the fission, as well as inducing the fission reactions...
, the principal reaction material in the second stage was uranium and plutonium. Similar to the Teller-Ulam configuration, a fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
device was used to create high temperatures and pressures in order to compress a second fissionable mass that would have otherwise been too large to sustain an efficient reaction if it were triggered with conventional explosives. This experiment was intended to develop intermediate yield weapons for expanding the inventory (around 1-2 Mt
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...
vs. 4-8).
Many "fusion" or "thermonuclear" weapons generate much, or even most, of their yields from fission. Although the U-238 isotope of uranium will not sustain a chain reaction, it still fissions when irradiated by the intense fast neutron flux of a fusion explosion. Because U-238 is plentiful and has no critical mass, it can be added in almost unlimited quantities as a "tamper" around a fusion bomb, helping to contain the fusion reaction and contributing its own fission energy. Fission of the U-238 tamper contributed 77% (8 megatons) to the yield of the 10.4 Mt Ivy Mike explosion.
Test execution
The most notable event of Operation Castle was the 'Castle BravoCastle Bravo
Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States ,...
' test. The dry fuel for 'Bravo' was 40% Li-6 and 60% Li-7. Only the Li-6 was expected to breed tritium for the deuterium-tritium fusion reaction; the Li-7 was expected to be inert. Yet J. Carson Mark
J. Carson Mark
J. Carson Mark was a Canadian-born American mathematician known especially for his work on developing nuclear weapons for the United States at Los Alamos National Laboratory.-Biography:...
, head of the Los Alamos Theoretical Design Division, had speculated that 'Bravo' could "go big", estimating that the device could produce an explosive yield as much as 20% more than had been originally calculated. Consequently, the Li-7 component turned out to be an excellent source of tritium through a previously unquantified reaction. In actuality, 'Bravo' exceeded expectations by 250%, yielding
Nuclear weapon yield
The explosive yield of a nuclear weapon is the amount of energy discharged when a nuclear weapon is detonated, expressed usually in the equivalent mass of trinitrotoluene , either in kilotons or megatons , but sometimes also in terajoules...
15 Mt
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...
-- 1,000 times more powerful than the Little Boy
Little Boy
"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...
weapon used on Hiroshima
Hiroshima
is the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshu, the largest island of Japan. It became best known as the first city in history to be destroyed by a nuclear weapon when the United States Army Air Forces dropped an atomic bomb on it at 8:15 A.M...
. Castle 'Bravo' remains to this day the largest atmospheric detonation ever conducted by the United States, and the seventh largest ever detonated in the world.
Because Castle 'Bravo' greatly exceeded its expected yield, JTF-7 was caught unprepared. Much of the permanent infrastructure on Bikini Atoll
Bikini Atoll
Bikini Atoll is an atoll, listed as a World Heritage Site, in the Micronesian Islands of the Pacific Ocean, part of Republic of the Marshall Islands....
was heavily damaged. The intense thermal flash ignited a fire at a distance of 20 nautical miles (37 km) on the island of Eneu (base island of Bikini Atoll). The ensuing fallout
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
contaminated all of the atoll, so much so, that it could not be approached by JTF-7 for 24 hours after the test, and even then exposure times were limited. As the fallout spread downwind to the east, more atolls were contaminated by radioactive calcium ash from the incinerated underwater coral banks. Although the atolls were evacuated soon after the test, 239 Marshallese on the Utirik
Utirik Atoll
Utirik Atoll or Utrik Atoll is a coral atoll of 10 islands in the Pacific Ocean, and forms a legislative district of the Ratak Chain of the Marshall Islands. Its total land area is only , but it encloses a lagoon with an area of...
, Rongelap
Rongelap Atoll
Rongelap Atoll or Namorik Atoll is a coral atoll of 61 islands in the Pacific Ocean, and forms a legislative district of the Ralik Chain of the Marshall Islands. Its total land area is only , but it encloses a lagoon with an area of...
, and Ailinginae Atoll
Ailinginae Atoll
Ailinginae Atoll is a coral atoll of 25 islands in the Pacific Ocean, on the northern end of the Ralik Chain of the Marshall Islands. Its total land area is only , but it encloses a lagoon of . It is located approximately west of Rongelap Atoll. The landscape is low-lying with only the top few...
s were subjected to significant levels of radiation. 28 Americans stationed on the Rongerik Atoll were also exposed. Follow-up studies of the contaminated individuals began soon after the blast as Project 4.1
Project 4.1
Project 4.1 was the designation for a medical study conducted by the United States of those residents of the Marshall Islands exposed to radioactive fallout from the March 1, 1954 Castle Bravo nuclear test at Bikini Atoll, which had an unexpectedly large yield...
, and though the short-term effects of the radiation exposure for most of the Marshallese were mild and/or hard to correlate, the long-term effects were pronounced. Additionally, 23 Japanese fishermen aboard Lucky Dragon No. 5
Daigo Fukuryu Maru
was a Japanese tuna fishing boat, which was exposed to and contaminated by nuclear fallout from the United States' Castle Bravo thermonuclear device test on Bikini Atoll, on 1 March 1954....
were also exposed to high levels of radiation. They suffered symptoms of radiation poisoning
Radiation poisoning
Acute radiation syndrome also known as radiation poisoning, radiation sickness or radiation toxicity, is a constellation of health effects which occur within several months of exposure to high amounts of ionizing radiation...
, and one crew member died in September 1954.
The heavy contamination and extensive damage from 'Bravo' significantly delayed the rest of the series. The post-'Bravo' schedule was revised on 14 April 1954.
| Experiment | Original date | Revised date | Original yield | Revised yield |
|---|---|---|---|---|
| UNION Castle Union Castle Union was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-14 thermonuclear weapon , one of the first deployed U.S... |
11 March 1954 | 22 April 1954 | 3-4 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
5-10 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
| YANKEE Castle Yankee Castle Yankee was the code name given to one of the tests in the Operation Castle series of American tests of thermonuclear bombs.-Jughead:... |
22 March 1954 | 27 April 1954 | 8 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
9.5 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
| NECTAR | 5 April 1954 | 20 April | 1.8 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
1-3 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
| ROMEO Castle Romeo Castle Romeo was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-17 thermonuclear weapon , the first deployed U.S... |
15 April 1954 | 27 March 1954 | 4 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
8 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
| KOON Castle Koon The Koon shot of Operation Castle was a test of a University of California Radiation Laboratory designed thermonuclear device.The 'dry' two-stage device was known as "Morgenstern". It was tested on 7 April 1954. The predicted yield of Morgenstern, which had a highly innovative secondary stage, was... |
22 April 1954 | 7 April 1954 | 1 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
1.5 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
The 'Romeo' and 'Koon' tests were complete by the time of this revision. The 'Echo' test was canceled due to the liquid fuel design becoming obsolete with the success of dry-fueled 'Bravo'. 'Yankee' was similarly considered obsolete and so was conducted using a Runt II device (similar to the 'Union' device) hastily completed at Los Alamos and flown to Bikini. With this revision, both of the "wet" fuel devices were removed from the test schedule.
As Operation Castle continued, the increased yields and fallout caused test locations to be re-evaluated. While the majority of the tests were planned for barges near the sand spit of Iroij, some were moved to the 'Bravo' and 'Union' craters. Additionally, Castle 'Nectar' was moved from Bikini Atoll to the Ivy 'Mike' crater at Eniwetok for expediency since Bikini was still heavily contaminated from the previous tests.
The final test in Operation Castle took place on 14 May 1954.
| Experiment | Date | Yield | Location |
|---|---|---|---|
| BRAVO Castle Bravo Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States ,... |
1 March 1954 | 15Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Reef off Nam Is, Bikini |
| ROMEO Castle Romeo Castle Romeo was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-17 thermonuclear weapon , the first deployed U.S... |
27 March 1954 | 11 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Barge in BRAVO crater, Bikini |
| KOON Castle Koon The Koon shot of Operation Castle was a test of a University of California Radiation Laboratory designed thermonuclear device.The 'dry' two-stage device was known as "Morgenstern". It was tested on 7 April 1954. The predicted yield of Morgenstern, which had a highly innovative secondary stage, was... |
7 April 1954 | 110 kt | Eneman, Bikini |
| UNION Castle Union Castle Union was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-14 thermonuclear weapon , one of the first deployed U.S... |
26 April 1954 | 6.9 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Barge off Iroij, Bikini |
| YANKEE Castle Yankee Castle Yankee was the code name given to one of the tests in the Operation Castle series of American tests of thermonuclear bombs.-Jughead:... |
5 May 1954 | 13.5 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Barge in UNION, Bikini |
| NECTAR | 14 May 1954 | 1.69 Mt TNT equivalent TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT... |
Barge Ivy-MIKE crater, Enewetak |
Results
Operation Castle was an unqualified success for the implementation of dry fuel devices. The Bravo design was quickly weaponized and is suspected to be the progenitor of the Mk-21Mark 21 nuclear bomb
The Mark 21 nuclear bomb was a United States nuclear gravity bomb first produced in 1955. It was based on the TX-21 "Shrimp" prototype that had been detonated during the Castle Bravo test in March 1954...
gravity bomb. The Mk-21 design project began on 26 March 1954 (just three weeks after Bravo) with production of 275 weapons beginning in late 1955. Romeo, relying on natural lithium, was rapidly turned into the Mk-17 bomb
Mark 17 nuclear bomb
The Mark 17 and Mark 24 were the first mass-produced hydrogen bombs deployed by the United States. The two differed in their "primary" stages. The MK 17/24 bombs were long, diameter. They weighed 21 tons. The Mark 17 had a yield in the range of 25 megatons TNT equivalent...
, the US first deployable H bomb, and was available to strategic forces as an Emergency Capability by mid-1954. Most of the Castle dry fuel devices eventually appeared in the inventory and ultimately grandfathered the majority of thermonuclear configurations.
In contrast, the Livermore
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
-designed Koon design was a failure. Using natural lithium and a heavily modified Teller-Ulam configuration, the test produced only 110 Kt of an expected 1.5 Mt
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...
. While engineers at the Radiation Laboratory had hoped it would lead to a promising new field of weapons, it was eventually determined that the design allowed premature heating of the lithium fuel, thereby disrupting the delicate fusion conditions.