Operation Castle

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Operation Castle was the highest-yield nuclear test series ever conducted by the United States.
Operation Castle was the highest-yield nuclear test series ever conducted by the United States.

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 is (largely) considered to be a success for the "dry fuel" design. One device failed to produce its predicted yield. 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, 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.

Contents

[edit] Background

AEC Authorization for Operation Castle
AEC Authorization for Operation Castle

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 (and therefore more real estate to stage experiments and support equipment upon). Both Atolls were part of the US Pacific Proving Grounds.

However, 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 Mt device tested at Eniwetok in 1951 leaving a crater approximately 1 mile (1.6 km) in diameter.[1]

The Ivy Mike test had been the world’s first thermonuclear explosion that used hydrogen fusion as its primary power source. The Mike device used cryogenic hydrogen isotopes in a liquid state, commonly referred to as a "wet bomb." The complex dewar mechanisms needed to store the liquid hydrogen made the device three stories tall and 82 tons in total weight—completely impractical to be delivered by contemporary weapon systems of the cold war.[2] With the success of Ivy Mike as a proof of concept, research began on using a solid state “dry fuel” to achieve a practical fusion weapon. The "dry fuel" concept used the Teller-Ulam design with lithium deuteride as the fusion fuel, greatly reducing the size, weight, and complexity. Operation Castle was chartered 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.

[edit] Experiments

Operation Castle was organized into 7 experiments, all but one which were to take place at Bikini Atoll. Below is the original test schedule (as of February 1954). [3]

Operation Castle Schedule
Experiment Device Prototype Fuel Date Predicted Yield Manufacturer Test Location
BRAVO Shrimp TX-21 40% Li-6 D (dry) 1 March, 1954 6 Mt Los Alamos Scientific Laboratory Reef off Nam Is, Bikini
UNION Alarm Clock EC-14 95% Li-6 D (dry) 11 March, 1954 3-4 Mt Los Alamos Scientific Laboratory Barge off Iroij, Bikini
YANKEE Jughead TX/EC-16 Cryo H-3 (wet) 22 March, 1954 8 Mt Los Alamos Scientific Laboratory Barge off Iroij, Bikini
ECHO Ramrod N/A Cryo H-3 (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 Los Alamos Scientific Laboratory Barge off Iroij, Bikini
ROMEO Runt TX/EC-17A 7.5% Li-6 D (natural) 15 April, 1954 4 Mt Los Alamos Scientific Laboratory Barge off Iroij, Bikini
KOON Morgenstern N/A 7.6% Li-6 D (natural) 22 April, 1954 1 Mt University of California Radiation Laboratory (Livermore) Eneman, Bikini


Operation Castle was intended to be a proof of concept for lithium deuteride fuels in fusion weapons. The so-called "dry" lithium-6 fuels were a significant advancement in weapon design over the liquid hydrogen used in the Ivy Mike device. Bravo and Union used enriched lithium in the Teller-Ulam configuration where a typical fission device is detonated in order to create the temperature and pressure needed for fusion in the lithium fuel capsule. Romeo and Koon used the same Teller-Ulam configuration, however, both were fueled by naturally occurring lithium deuteride (92% Li-7, 7.5% Li-6). The natural fuels, being vastly less time and resource intensive to obtain compared to enriched lithium, were important for US's ability expand the nuclear stockpile during the cold war arms race.

Because the viability of dry fuels was not known, and there was significant risk of failure, development of liquid isotope weapons continued in parallel. Even though they were considered less practical due to logistical problems with transport, handling, and storage of a cryogenic device, the cold war arms race drove a technical demand for a viable weapon. Echo and Yankee were liquid fuel designs that were greatly reduced in size and weight over their Ivy Mike predecessor. The Jughead device was ultimately weaponized, despite the liquid fuel draw-backs, 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).

[edit] Test execution

The most notable event of Operation Castle was the Bravo test. The dry fuel for Bravo was 40% enriched Li-6, and 60% naturally occurring Li-7, the latter of which was expected to be essentially 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.[4] Unexpectedly, the Li-7 was not inert, but extremely reactive under fusion conditions and produced a very high neutron and energy surplus through a previously unquantified neutron reaction. The result was that Bravo exceeded its expected yield by more than 250%, totaling 15 Mt or 1,000 times more powerful than the Little Boy weapon used on Hiroshima. Bravo is to this day the largest detonation ever conducted by the United States, and the seventh largest ever detonated in the world.

Because Bravo exceeded its designed yield by such a large margin, the 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 on the island of Eneu (base island of Bikini Atoll).[5] The ensuing fallout contaminated all of the Atoll to various levels, 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.[6] As the fallout spread downwind, more atolls were contaminated with activated calcium ash. Although people on the atolls were evacuated soon after the test, in the end 239 Marshallese on the Utirik, Rongelap, and Ailinginae Atolls were subjected to significant levels of radiation, and 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 of 1954.

The heavy contamination and extensive damage from Bravo caused significant delays in the conduct the rest of the series. The post-Bravo schedule was revised on 14 April 1954[7].

Operation Castle Schedule (Post BRAVO)
Experiment Original Date Revised Date Original Yield Revised Yield
UNION 11 March, 1954 22 April, 1954 3-4 Mt 5-10 Mt
YANKEE 22 March, 1954 27 April, 1954 8 Mt 9.5 Mt
NECTAR 5 April, 1954 20 April 1.8 Mt 1-3 Mt
ROMEO 15 April, 1954 27 March, 1954 4 Mt 8 Mt
KOON 22 April, 1954 7 April, 1954 1 Mt 1.5 Mt


The Romeo and Koon tests were complete by the time of this revision. The Echo test was canceled due to the liquid fuel design being considered obsolete following the success of the dry fuel in Bravo. The Jughead device was similarly considered obsolete and the Yankee test 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 from the dry fuel experiments 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, Nectar was moved from Bikini Atoll to the Ivy Mike crater at Enewetak as a means of expediency since Bikini was still heavily contaminated from the previous tests.[8]

The final test in Operation Castle took place on 14 May 1954.

Operation Castle (Actual)
Experiment Date Yield Location
BRAVO 1 March, 1954 15Mt Reef off Nam Is, Bikini
ROMEO 27 March, 1954 11 Mt Barge in BRAVO crater, Bikini
KOON 7 April, 1954 110 kt Eneman, Bikini
UNION 26 April, 1954 6.9 Mt Barge off Iroij, Bikini
YANKEE 5 May, 1954 13.5 Mt Barge in UNION, Bikini
NECTAR 14 May, 1954 1.69 Mt Barge Ivy-MIKE crater, Enewetak

[edit] Results

Bikini Atoll in the summer 1954 after the completion of Operation Castle.
Bikini Atoll in the summer 1954 after the completion of Operation Castle.

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-21 gravity bomb. The Mk-21 design project began on 26 March 1954 (just three weeks after Bravo) with production of 275 weapons beginning in the fall of 1955. Romeo, relying on natural lithium, was rapidly turned into the Mk-17 bomb, the US first H bomb [9], and was available to strategic forces as an Emergency Capability by late summer of 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.

[edit] See also

[edit] References

  1. ^ Operation Ivy, pg 192
  2. ^ Dark Sun, pg 495.
  3. ^ Castle Series, pg 247
  4. ^ O'Keefe, page 179
  5. ^ Castle Series, pg 209
  6. ^ Hacker, pg 140
  7. ^ Castle Series pg 268
  8. ^ Castle Series pg 248.
  9. ^ Development of the Mk 17 bomb, Atomic Museum.com

[edit] Bibliography

  • The United States Department of Defense; Defense Nuclear Agency (1982). Castle Series. Washington DC: United States Government Printing Office. 
  • The United States Department of Defense; Defense Nuclear Agency (1983). Operation Ivy--1952. Washington DC: United States Government Printing Office. 
  • Rhodes, Richard (1995). Dark Sun. New York, New York: Simon & Schuster. 
  • O'Keefe, Bernard J. (1983). Nuclear Hostages. Boston: Houghton Mifflin Company. 
  • Hacker, Barton C (1994). Elements of Controversy: The Atomic Energy Commission and Radiation Safety in Nuclear Weapons Testing. Los Angeles: University of California Press. 

[edit] External links

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