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Operation Crossroads
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Operation Crossroads was a series of nuclear weapon tests conducted by the United States at Bikini Atoll in the summer of 1946. Its purpose was to test the effect of nuclear weapons on naval ships. The series consisted of two detonations, each with a yield of 23 kilotons: Able was detonated at an altitude of 520 feet (158 m) on 1 July 1946; Baker was detonated 90 feet (27 m) underwater on 25 July 1946.
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Operation Crossroads was a series of nuclear weapon tests conducted by the United States at Bikini Atoll in the summer of 1946. Its purpose was to test the effect of nuclear weapons on naval ships. The series consisted of two detonations, each with a yield of 23 kilotons: Able was detonated at an altitude of 520 feet (158 m) on 1 July 1946; Baker was detonated 90 feet (27 m) underwater on 25 July 1946. A third planned burst, Charlie, was canceled.
The Crossroads tests were the fourth and fifth nuclear explosions done by the USA (following the Trinity test and the bombings of Hiroshima and Nagasaki). They were the first nuclear tests held in the Marshall Islands, and the first to be publicly announced beforehand and observed by an audience of invited witnesses and a large press corps.
Operation Crossroads added a new word to the languages of the world: "bikini" as the name for a woman's two-piece bathing suit.
Ultimately, the biggest news from Crossroads, not widely reported at the time, was the radioactive contamination of all the target ships by the Baker shot. It was the world's first experience with immediate, concentrated local radioactive fallout from a nuclear explosion. (The global fallout from an air burst is delayed and widely dispersed.)
Preparation
When World War II ended, there had been no controlled tests of the toxicity and residual effects of atomic bomb detonations; and information was lacking concerning the effects of atomic bombs on ships and military equipment with respect to methods for defense against such effects. As the United States demobilized its wartime military infrastructure, there was debate regarding the future size and composition of the armed forces. Some believed the atomic bomb made navies obsolete. Senator Brien McMahon said on 25 August 1945: "In order to test the destructive powers of the atomic bomb against naval vessels, I would like to see these Japanese naval ships taken to sea and an atomic bomb dropped on them."
A series of three tests was recommended to study the effects of nuclear weapons on ships, equipment, and material. Test site requirements were specified:
- A protected anchorage at least six miles wide
- A site which was uninhabited, or nearly so
- A location at least 300 miles from the nearest city
- Weather patterns without severe cold and violent storms
- Predictable winds directionally uniform from sea level to 60,000 feet
- Predictable water currents away from shipping lanes, fishing areas, and inhabited shores
- Controlled by the United States
Timing became critical because Navy manpower required to move the ships was being released from active duty, and civilian scientists knowledgeable about atomic weapons were leaving federal employment for college teaching positions requiring their attendance when the fall semester started.
Joint Task Force One (JTF-1) was created, with a ten-month tenure, to conduct the tests at Bikini Atoll. Vice Admiral William H. P. Blandy was its commander. Dress rehearsals were conducted with dynamite and model ships in a pond named "Little Bikini" on the grounds of the David Taylor Model Basin outside Washington, D.C. At Bikini 100 tons of dynamite were used to remove coral heads from the lagoon and make room for the target ships.
The native population of 167 was moved 128 miles east to the uninhabited Rongerik Atoll, to begin a so far permanent exile. (Three Bikini families returned in 1974 but were evacuated again in 1978 because of radioactivity in their bodies from four years of eating contaminated food. The atoll remains unpopulated.)
Ships
A fleet of more than 90 vessels was assembled in Bikini Lagoon as a target. At the center of the target cluster, the density was 20 ships per square mile, three to five times greater than military doctrine would allow. The goal was not to duplicate a realistic anchorage, but to measure damage as a function of distance at as many different distances as possible.
The target fleet included four obsolete U.S. battleships, two aircraft carriers, two cruisers, eleven destroyers, eight submarines, numerous auxiliary and amphibious vessels, and three surrendered German and Japanese ships. Military equipment was arrayed on some of the ships, and amphibious craft were berthed on Bikini Island. Technical experiments were also conducted to study nuclear weapon explosion phenomena.
Some experiments included the use of live animals. Bikini support ship USS Burleson (APA-67) brought 200 pigs, 60 guinea pigs, 204 goats, 5000 rats, 200 mice, and grains containing insects to be studied for genetic effects by the National Cancer Institute.
A support fleet of more than 150 ships provided quarters, experimental stations, and workshops for most of the 42,000 men (more than 37,000 of whom were Navy personnel) and the 37 women nurses. Additional personnel were located on nearby atolls such as Eniwetok and Kwajalein. Navy personnel were allowed to extend their obligated service for one year if they wanted to participate in the tests and see an atomic bomb explode. Many of the civilian scientists also volunteered for project participation to see an atomic bomb explode. The islands of the Bikini Atoll were used as instrumentation sites and, until Baker contaminated them, as recreation sites.
Cameras
Radio-controlled autopilots were installed in eight B-17 bombers, converting them into remote-controlled drones which were then loaded with automatic cameras, radiation detectors, and air sample collectors. Their pilots operated them from mother planes at a safe distance from the detonations. The drones were able to fly into radiation environments, such as Able's mushroom cloud, which would be lethal to live crew members.
All the land-based detonation-sequence photographs were taken by remote control from tall towers erected on several islands of the atoll. In all, Bikini cameras would take 50,000 still pictures and 1,500,000 feet of motion picture film. One of the cameras could shoot 1,000 frames per second.
Before the first test, all personnel were evacuated from the target fleet and Bikini Atoll. They boarded ships of the support fleet, which took safe positions at least 10 nautical miles (18.5 km) east of the atoll. Test personnel were issued special dark glasses to protect their eyes, but a decision was made shortly before test Able that the glasses might not be protective; and personnel were instructed to turn away from the blast, shut their eyes, and cradle their arm across their face for additional protection. A few observers who disregarded the recommended precautions advised the others when the bomb detonated. Most shipboard observers reported feeling a slight concussion and hearing a disappointing little "poom".
Nicknames
"Able" and "Baker" are the first two letters of the Joint Army/Navy Phonetic Alphabet, used from 1941 until 1956. "Alfa" and "Bravo" are their counterparts in the current NATO phonetic alphabet. "Charlie" is the third letter in both systems. According to eyewitness accounts, the time of detonation for each test was announced as "H" or "How" hour; in the official JTF-1 history, the term "M" or "Mike" hour is used instead.
The two bombs were copies of the plutonium-implosion Fat Man bomb dropped on Nagasaki. They were given nicknames which have largely been forgotten. The Able bomb was called Gilda and decorated with the likeness of Rita Hayworth, star of the 1946 movie Gilda. The Baker bomb was Helen of Bikini. This femme-fatale theme for nuclear weapons, combining seduction and destruction, is epitomized by the use in all languages, starting in 1946, of bikini as the name of for woman's two-piece bathing suit.
The plutonium core used in "Gilda" had been previously nicknamed the "Demon core" by scientists at Los Alamos after it twice went critical in experiments in 1945 and 1946. In each instance, it killed a scientist.
Test Able - July 1
At 0900 the weapon was dropped from the B-29 Superfortress Dave's Dream (formerly Big Stink of the 509th Composite Group) and detonated 520 ft above the target fleet, with a yield of 23 kilotons. Five ships were sunk. Two attack transports sank immediately, two destroyers within hours, and one Japanese cruiser the following day. It was the first time more than one ship had been sunk by a single bomb.
Some of the 114 press observers expressed disappointment at the effect on ships. The New York Times reported, prematurely, that "only two were sunk, one capsized, and eighteen damaged." The next day, the Times carried an explanation by Secretary of the Navy James Forrestal that "heavily built and heavily armored ships are difficult to sink unless they sustain underwater damage."
However, the main cause of less-than-expected ship carnage was that the bomb missed its aim point by 710 yards. The ship the bomb was aimed at failed to sink. The miss resulted in a government investigation of the flight crew of the B-29 bomber. Eventually, it was agreed that a flaw in the bomb's tail stabilizer had caused the miss, and the flight crew was cleared of responsibility.
The battleship Nevada had been designated as the aim point for Able and was painted red, with white gun barrels and gunwales, to make it stand out in the central cluster of target ships. There were eight ships within 400 yards of it. Had the bomb exploded over the Nevada as planned, at least nine ships, including two battleships and an aircraft carrier, would likely have sunk. The actual detonation point, west northwest of the target, was closer to the attack transport Gilliam, in much less crowded water.
Able target array
Ships sunk - Yards from surface zero | # | Name | Type | Distance |
|---|
| 5 | Gilliam | Transport | 50 | | 9 | Sakawa | Japanese Cruiser | 420 | | 4 | Carlisle | Transport | 430 | | 1 | Anderson | Destroyer | 600 | | 6 | Lamson | Destroyer | 760 | |
In addition to the five ships that sank, fourteen were judged to have serious damage or worse, most due to the bomb's air-pressure shock wave. All but three were located within 1,000 yards of the detonation. Inside that radius, orientation to the bomb was a factor in shock wave impact. For example, ship #6, the destroyer Lamson, which sank, was farther away than seven ships that stayed afloat. Lamson was broadside to the blast, taking the full impact on its port side, while the seven closer ships were anchored with their sterns toward the blast, somewhat protecting the most vulnerable part of the hull.
The only large ship inside the 1,000-yard radius which sustained moderate, rather than serious, damage was the Japanese battleship Nagato, ship #7. Sturdily built, its stern-on orientation to the bomb gave it some protection. Also, unrepaired damage from World War II may have complicated damage analysis. As the ship from which the Pearl Harbor attack had been commanded, Nagato was positioned near the aim point to guarantee its being sunk. Since the Able bomb missed its target, that symbolic sinking would come three weeks later, in the Baker shot.
Serious damage to ship #10, the aircraft carrier Saratoga, more than a mile from the blast, was due to fire. For test purposes, all the ships carried realistic amounts of fuel and ordnance, plus airplanes. Most warships carried a seaplane on deck, which could be lowered into the water by crane, but an aircraft carrier was loaded with airplanes and highly volatile aviation fuel, both on deck and in the hangers below. The fire was extinguished and the Saratoga was kept afloat for use in the Baker shot.
For a "soft" urban target like Hiroshima, anything as close to the bomb as the Saratoga would be on the edge of the 5 psi lethal area, inside a firestorm over two miles wide. But water doesn't burn, and warships, other than aircraft carriers, are extremely resistant to blast and fire.
Radiation
As with all three previous nuclear detonations -- Trinity, Little Boy (Hiroshima), and Fat Man (Nagasaki) -- the Crossroads Able shot was an air burst, detonating high enough in the air to prevent surface materials from being drawn into the fireball. With an air burst, the radioactive fission products rise into the stratosphere and become part of the global, rather than the local, environment. Air bursts were officially described as "self-cleansing." There was no significant local fallout.
There was, however, an intense transitory burst of fireball radiation lasting a few seconds. Many of the closer ships received doses of neutron and gamma radiation that could have been lethal to anyone on the ship, but the ships themselves did not become radioactive, except by neutron activation of materials in the ships, which was judged to be a minor problem (by the standards of the time). Within a day nearly all the surviving target ships had been reboarded. The ship inspections, instrument recoveries, and remooring necessary for the Baker test proceeded on schedule.
Fifty-seven guinea pigs, 109 mice, 146 pigs, 176 goats, and 3030 white rats had been placed on 22 target ships in stations normally occupied by people. Ten percent of the animals were killed by the air blast, fifteen percent were killed by radioactivity, and ten percent were killed during later study. Altogether, 35% of the animals died as a direct result of blast or radiation exposure.
The high rate of test animal survival was due in part to the nature of single-pulse radiation. As with the two Los Alamos criticality accidents involving the Able core, victims who were close enough to receive a lethal dose died, those farther away recovered and survived. Also, all the rats were placed outside the expected lethal zone in order to study possible mutations in future generations. Since rats made up 86% of the total, obviously not all of them survived.
Although the Able bomb missed its target, Nevada, by nearly half a mile, and it failed to sink or to contaminate the battleship, goat #119, tethered inside a gun turret and shielded by armor plate, received enough fireball radiation to die four days later of radiation sickness. Had the Nevada been fully manned, she would likely have become a floating coffin, dead in the water for lack of a live crew.
Test Baker - July 25
In Baker, the weapon was suspended beneath landing craft LSM-60 anchored in the midst of the target fleet. Baker was detonated 90 feet (27 m) underwater, halfway to the bottom in water 180 feet (54 m) deep. How/Mike Hour was at 0835. No identifiable part of LSM-60 was ever found. Ten ships were sunk, including a German heavy cruiser which sank in December, five months after the test, because radioactivity prevented repairs to a leak in the hull.
Photographs of Baker are unique among nuclear detonation pictures. The blinding flash that usually obscures the target area took place underwater and was barely seen. The clear image of ships in the foreground and background gives a sense of scale. The large Wilson cloud and the vertical water column are distinctive Baker shot features, making the pictures easily identifiable. The most famous picture shows the 27,000 ton battleship Arkansas, long, upended to near vertical, with two-thirds of its length in the air, silhouetted against the north face of the water column.
As with Able, any ships that remained afloat within 1,000 yards of the detonation were seriously damaged, but this time the damage came from below, from water pressure rather than air pressure. The greatest difference between the two shots, however, was the radioactive contamination of all the target ships by Baker.
Baker target array
Ships sunk - Yards from surface zero | # | Name | Type | Distance |
|---|
| 50 | LSM-60 | Amphibious | 0 | | 3 | Arkansas | Battleship | 170 | | 8 | Pilotfish | Submarine | 363 | | 10 | Saratoga | A/C Carrier | 450 | | 12 | YO-160 | Yard Oiler | 520 | | 7 | Nagato | Battleship | 770 | | 41 | Skipjack | Submarine | 800 | | 2 | Apogon | Submarine | 850 | | 11 | ARDC-13 | Drydock | 1,150 | | 36 | Prinz Eugen | Cruiser | 1,800 | |
The German heavy cruiser Prinz Eugen survived both the Able and Baker tests but was too radioactive to have leaks repaired. In September 1946 she was towed to Kwajalein Atoll where she capsized in shallow water on 22 December 1946, five months after Baker. She remains there today, with starboard propeller blades in the air.
The submarine Skipjack was the only sunken ship successfully raised at Bikini. She was towed to California and sunk again, as a target ship off the coast, two years later.
Three other ships, all in sinking condition, were towed ashore at Bikini and beached: attack transport Fallon, ship #25; destroyer Hughes, ship #27; and submarine Dentuda, ship #24. Dentuda, being submerged (thus avoiding the base surge) and outside the 1,000-yard circle, escaped serious contamination and hull damage and was successfully decontaminated, repaired, and briefly returned to service.
Sequence of blast events
The Baker shot produced so many unusual phenomena that two months later a conference was held to standardize nomenclature and define new terms for use in descriptions and analysis.
The underwater fireball took the form of a rapidly expanding hot "gas bubble" which pushed against the water, generating a supersonic, hydraulic shock wave which crushed the hulls of nearby ships as it spread out. Eventually it slowed to the speed of sound in water, which is one mile per second, five times faster than sound in air. On the surface, the shock wave was visible as the leading edge of a rapidly expanding ring of dark water, called the "slick" for its resemblance to an oil slick. Close behind the slick was a visually more dramatic, but less destructive whitening of the water surface called the "crack."
When the gas bubble's diameter equaled the water depth, 180 feet, it hit the sea floor and the sea surface simultaneously. At the bottom, it started digging a shallow crater, ultimately 30 feet deep and 2,000 feet wide. At the top, it pushed the water above it into a "spray dome," which burst through the surface like a geyser. Elapsed time since detonation was four milliseconds.
During the first full second, the expanding bubble removed all the water within a 500-foot radius and lifted two million tons of spray and seabed sand into the air. As the bubble rose at 2,500 feet per second, it stretched the spray dome into a hollow cylinder or chimney of spray called the "column," 6,000 feet tall, 2,000 feet wide, and with walls 300 feet thick.
As soon as the bubble reached the air, it started a supersonic atmospheric shock wave which, like the crack, was more visually dramatic than destructive. Brief low pressure behind the shock wave caused instant fog which shrouded the developing column in a "Wilson cloud", also called a "condensation cloud", obscuring it from view for two seconds. The Wilson cloud started out hemispherical, expanded into a disk which lifted from the water, revealing the fully developed spray column, then expanded into a doughnut and vanished.
The Able shot also produced a Wilson cloud, but heat from the fireball dried it out more quickly.
By the time the Wilson cloud vanished, the top of the column had become a "cauliflower," and all the spray in the column and its cauliflower was moving down, back into the lagoon. Although cloudlike in shape, the cauliflower was more like the top of a geyser where water stops moving up and starts to fall. There was no mushroom cloud; nothing rose into the stratosphere.
Image:Crossroads baker explosion.jpg|Crossroads Baker, showing the white surface "crack" under the ships, and the top of the hollow spray column protruding through the hemispherical Wilson cloud. Bikini Island beach in the background.
Image:Crossroads Baker (wide-zoom).jpg|The most famous Baker picture. The Wilson cloud has lifted revealing the fully formed spray column, with the upended battleship Arkansas, right side, falling back into its northern perimeter.
Image:Operation Crossroads Baker.jpg|The Wilson cloud has evaporated revealing the cauliflower atop the spray column. Two million tons of water spray fall back into the lagoon. The radioactive base surge is moving toward the ships.
Meanwhile, lagoon water rushing back into the space vacated by the rising gas bubble started a tsunami-like water wave which lifted the ships as it passed under them. At 11 seconds after detonation, the first wave was 1,000 feet from surface zero and 94 feet high. By the time it reached the Bikini Island beach, 3.5 miles away, it was a nine-wave set with shore breakers up to 15-feet high, which tossed landing craft onto the beach and filled them with sand.
Twelve seconds after detonation, falling water from the column started to create a 900-foot tall "base surge" resembling the mist at the bottom of a large waterfall. Unlike the water wave, the base surge rolled over rather than under the ships. Of all the bomb's effects, the base surge had the greatest consequence for most of the target ships, because it painted them with radioactivity that could not be removed.
Battleship Arkansas
Arkansas was the closest ship to the bomb other than the ship it was suspended from. The underwater shock wave crushed the starboard side of its hull, which faced the bomb, and rolled the battleship over onto its port side. It also ripped off the two starboard side propellers and their shafts, along with the rudder and part of the stern, shortening the hull by 25 feet. Some target ships carried gyroscopic pitch and roll recorders; if the Arkansas had any such devices they were not retrieved. There is no record of what happened to the ship during the two seconds when the Wilson cloud blocked any view of the site.
At 562 feet long, the battleship was three times as long as the water is deep. When the Wilson cloud lifted, the Arkansas was apparently bow-pinned to the sea floor with its truncated stern 350 feet in the air. Unable to sink straight down in the relatively shallow lagoon, it toppled backward into the water curtain of the spray column.
She was next seen by Navy divers, the same year, lying upside down with her bow on the rim of the underwater bomb crater and stern angled toward the center. There was no sign of the superstructure or the big guns. The first diver to reach the Arkansas sank up to his armpits in radioactive mud. When National Park Service divers returned in 1989 and 1990, the bottom was again firm-packed sand, and the mud was gone. They were able to see the barrels of the front guns, which had not been visible in 1946.
All large naval gunships are top heavy and settle upside down when they sink, a notable exception being the Bismarck. The Arkansas settled upside down, but a 1989 diver's sketch of the wreck shows hardly any of the starboard side of the hull, making it look like the ship is lying on its side. Most of the starboard side is there, but severely compacted.
The superstructure has not been found. It was either stripped off and swept away or is lying under the hull, crushed and buried under sand which flowed back into the crater, partially refilling it. The only diver access to the inside is a tight squeeze through the port side casemate, called the "aircastle." The Park Service divers practiced on the similar aircastle of battleship Texas, a museum ship, before entering the Arkansas in 1990.
Image:Battleship Arkansas diver sketch (small image).png|Battleship Arkansas upside down, 180 feet deep in Bikini Lagoon. Diver's sketch from a 1989 National Park Service dive.
Image:Battleship Arkansas aircastle.jpg|Port aircastle of the Arkansas in 1989, upside down against the bottom. The only diver's access into the ship, it was entered in 1946 and again in 1990.
Image:USS Texas BB-35 aircastle.jpg|A similar battleship, Texas, with aircastle circled. At Bikini, everything that was above Arkansass lower deck guns is either missing or is buried in the sand.
Aircraft Carriers
Saratoga sank eight hours after the underwater shock wave opened up leaks in the hull. Immediately after the shock wave passed, the water wave lifted the stern 43 feet and the bow 29 feet, rocked the ship side to side, and crashed over it, sweeping all five moored airplanes off the flight deck, and knocking the stack over onto the deck. She remained upright and outside the spray column, but close enough to be drenched by radioactive water from the collapsing cauliflower head, as well as by the base surge.
Admiral Blandy ordered tugs to tow the carrier to Enyu island for beaching, but Saratoga and the surrounding water remained too radioactive for close approach until after she sank. She settled upright on the bottom, with the top of her mast forty feet below the surface. Today, with radioactivity at safe levels for sport diving, Saratoga is the star attraction of a struggling, high-end sport diving industry. (The 2009 diving season was canceled because of fuel costs, unreliable airline service to the island, and a decline in the Bikini Islanders' trust fund which subsidized the operation.)
Independence survived Able with spectacular damage to the flight deck. She was moored far enough away from Baker to avoid further physical damage, but was severely contaminated. She was towed to San Francisco, where four years of decontamination experiments at the Hunters Point Naval Shipyard failed to produce satisfactory results. On January 29, 1951, she was scuttled in the ocean near the Farallon Islands.
Image:Carrier_Saratoga_diver_sketch.png|Diver's sketch of Saratoga on the bottom of Bikini Lagoon. Starboard torpedo blister is crumpled.
Image:USS Independence (CVL-22) burning.png|Independence, ship #28, showing blast damage from Able, before Baker made her radioactive.
Fission-product radioactivity
Baker was the first nuclear explosion close enough to the surface to keep the radioactive fission products in the local environment. It was not self-cleansing. The result was radioactive contamination of the lagoon and the target ships. While anticipated, it caused far greater problems than were expected.
The Baker explosion produced about two pounds of fission products, equivalent in radioactivity to hundreds of tons of radium. These fission products were thoroughly mixed with the two million tons of spray and seabed sand that were lifted into the spray column and its cauliflower head and then dumped back into the lagoon. Most of it stayed in the lagoon and settled to the bottom or was carried out to sea by the lagoon's internal tidal and wind-driven currents.
A small fraction of the contaminated spray was thrown back into the air as the base surge. Unlike the Wilson cloud, a meteorological phenomenon in clean air, the base surge was a heavy fog bank of radioactive mist that rolled across all the target ships, painting their surfaces with fission products. When the mist in the base surge evaporated, the base surge became invisible but continued to move away, contaminating ships several miles from the detonation point.
Unmanned drone boats were the first vessels to enter the lagoon. Onboard instruments allowed remote-controlled radiation measurements to be made. When support ships entered the lagoon for evaluation, decontamination, and salvage activities, they steered clear of lagoon water hot spots detected by the drone boats.
The standard for radiation exposure to personnel was the same as that used by the Manhattan Project, 0.1 roentgens per day. Because of this constraint, only the five most distant target ships could be boarded on the first day. The closer-in ships were hosed down by navy fireboats using saltwater and foamite. The first hosing reduced radioactivity by half, but subsequent hosings were ineffective. For most of the ships, reboarding had to wait until the short-lived radioisotopes decayed; ten days elapsed before the last of the targets could be boarded.
In the first six days after Baker, when radiation levels were highest, 4,900 men boarded target ships. Sailors tried to scrub off the radioactivity with brushes, water, soap, and lye. Nothing worked, short of sandblasting to bare metal.
Image:Crossroads Baker Base Surge.jpg|As the spray column falls, a radioactive "base surge," like mist at the bottom of a waterfall, moves out toward the target ships. Foreground ship (left) is the 725-foot-long Japanese battleship Nagato.
Image:Crossroads Baker Hosedown.jpg| In a largely ineffective effort to wash off base surge contamination, a navy fireboat hoses down the battleship New York with radioactive lagoon water. The ship was outside the area shown by the map above.
Image:Crossroads Baker Scrubdown.jpg|Sailors scrubbing down the German cruiser Prinz Eugen with brushes, water, soap, and lye. Five months later, the ship was still too radioactive to permit repairs to a leak, and she sank.
Induced radioactivity and plutonium
The Baker explosion ejected into the environment about twice as many free neutrons as there were fission events. In an air burst, most of these environmental neutrons are absorbed by superheated air which rises into the stratosphere, along with the fission products and unfissioned plutonium. In the underwater Baker detonation, they were captured by seawater in the lagoon. Of the four major elements in seawater – hydrogen, oxygen, sodium, and chlorine – only sodium becomes radioactive with the addition of a single neutron to its nucleus. Common sodium-23 becomes radioactive sodium-24, with a 15-hour half-life. (In six days its intensity drops a thousand fold, but the flip side of short half-life is high intensity at the beginning.)
A small fraction of one pound of radioactive sodium was produced, but unlike fission products, which are heavy and eventually sank to the bottom of the lagoon, the sodium stayed in solution. It contaminated the hulls and onboard saltwater systems of support ships that entered the lagoon, and it contaminated the water used in decontamination.
Finally, the 11.6 pounds of plutonium which did not undergo fission were mixed in with the two pounds of fission products. Plutonium produces alpha radiation which cannot penetrate skin, and is not a biological hazard unless ingested or inhaled. It could not be detected by the film badges and Geiger counters used by people who boarded the target ships, but the assumption was made that if the gamma rays coming from fission products were not detected, no plutonium would be present either. This was discovered not to be the case. Plutonium turned up on the Prinz Eugen in places not contaminated by fission products.
Test animals
Only pigs and rats were used in the Baker test. All the pigs and most of the rats died. Radiation from a contaminated environment is continuous and cumulative. With the Able test, lethality was determined by proximity to the fireball and its pulse of radiation. With Baker, lethality was determined by the amount of time spent aboard contaminated ships. Several days elapsed before sailors were able to reboard the target ships where test animals were located; during that time the accumulated doses became lethal for the animals.
Test Charlie
Charlie was to explode deep under the surface in the lee of the atoll to test effects on unmoored ships. Charlie would have tested the effects of using nuclear weapons as depth charges. Technical support personnel were unavailable because of the unanticipated decontamination delay following test Baker. There were no uncontaminated target ships available for use in Charlie. The official reason for canceling Charlie was that it was felt unnecessary after the success of the Able and Baker tests, and it was deemed less pressing when the entire US arsenal had only a handful of such weapons. The test intended for Charlie was conducted in 1955 as Operation Wigwam.
Crossroads Followup
The inability to complete inspections on much of the target fleet threatened the success of the operation after Baker. The program of target vessel decontamination was begun in earnest about August 1. This involved washing the ships' exteriors using work crews drawn from the target ships' companies under radiological supervision of monitors equipped with radiation detection and measurement devices. Initially, decontamination was slow because the safe time aboard the target ships was measured only in minutes.
By August 3, fission-product contamination in the lagoon water had decayed or settled out sufficiently that it was no longer necessary for support ships to sample lagoon water as they moved about. An oil slick, which trapped contamination at the surface, had drifted north, across the reef west of Bikini island and several miles out to sea, all during the first day, July 25. However, by August 4, the radioactive oil slick had returned and come ashore on the north side of Bikini island. Meanwhile, the support fleet was accumulating contamination from low-level radioactivity in marine growth on the ships' hulls and seawater piping systems.
By August 10, a decision was made to stop work in Bikini and tow the surviving target fleet to Kwajalein Atoll where the work could be done in uncontaminated water. The move was accomplished during the remainder of August and September, but decontamination work ceased in September. A major task at Kwajalein, after decontamination work was abandoned, was to offload ammunition stored aboard the target ships. This work continued into the fall of 1946. Personnel continued to work on target ships at Kwajalein into 1947.
Eight of the major ships and two submarines were towed back to the United States and Hawaii for radiological inspection. Twelve target ships were so lightly contaminated that they were remanned and sailed back to the United States by their crews. Ultimately, only nine target ships were able to be scrapped rather than scuttled. The remaining target ships were destroyed by sinking off Bikini or Kwajalein Atolls, or near the Hawaiian Islands or the California coast during 1946-1948.
The support ships were decontaminated as necessary and received a radiological clearance before they could return to the fleet. This required a great deal of experimentation at Navy shipyards in the United States, primarily at San Francisco, California. The destroyer Laffey required "sandblasting and painting of all underwater surfaces, and acid washing and partial replacement of salt-water piping and evaporators."
Finally, a formal resurvey was conducted in the summer of 1947 to study long-term effects of the Crossroads tests. According to the official report, decontamination efforts "revealed conclusively that removal of radioactive contamination of the type encountered in the target vessels in test Baker cannot be accomplished successfully."
On August 11, 1947, Life Magazine summarized the report in a 14-page article with 33 pictures. The article stated, "If all the ships at Bikini had been fully manned, the Baker Day bomb would have killed 35,000 crewmen. If such a bomb were dropped below New York's Battery in a stiff south wind, 2 million people would die." Although it was accurately written, a casual reader of the article may have confused the grisly effects of Able's transitory fireball radiation on the close-in test animals with the equally deadly but more widespread and persistent contamination from Baker's base surge. Aside from the Life article, the report received little public attention.
The contamination problem was not widely appreciated by the general public until 1948, when No Place to Hide, a best-selling book by David Bradley, M.D., was serialized in the Atlantic Monthly, condensed by the Reader's Digest, and selected by Book-of-the-Month-Club. In his preface, Bradley, a key member of the Radiological Safety Section at Bikini known as the "Geiger men," asserted that "the accounts of the actual explosions, however well intended, were liberally seasoned with fantasy and superstition, and the results of the tests have remained buried in the vaults of military security." His description of the Baker test and its aftermath brought to world attention the problem of radioactive fallout from nuclear weapons.
Exposure to Personnel
All Crossroads operations were undertaken with radiological supervision intended to keep personnel from being exposed to more than 0.1 röntgen (R) per day. At the time, this was considered to be an amount of radiation that could be tolerated for long periods without any harmful effects on health.
Radiological supervision included predicting areas of possible danger, providing trained personnel equipped with radiation survey instruments to act as guides during operations involving potential exposure, and elaboration of rules and regulations governing conduct in these operations. Personnel were removed for one or more days from areas and activities of possible exposure if their badges showed more than 0.1 R / day exposure.
About 15% of the JTF 1 personnel was issued at least one of the 18,875 film-badge dosimeters during Crossroads. Approximately 6,596 personnel were on the islands or ships that had no potential for radiation exposure. Personnel anticipated to be at the greatest radiological risk were badged, and a percentage of each group working in less contaminated areas was badged. The maximum accumulated exposure recorded was 3.72 R, received by a radiation safety monitor.
Lacking complete radiation exposure data, reconstructions have been made of all personnel exposures for unbadged crewmembers of the ships involved. These calculations have considered the several sources of radiation at work in Bikini, such as the low-level contamination in the lagoon water, living aboard support ships, and boarding the contaminated target ships. The calculations relied upon radiation measurements recorded by radiation safety personnel in 1946. This data was used in a computer model that includes such factors as the radiation-shielding properties of ships' hulls and realistic patterns of daily personnel activity on weather decks and below. The actual movements of each ship were then used to reconstruct a dose for the crew. Calculated exposures range from 0 to 2.5 rem (25 mSv) (gamma) for support ships. Exposures for target ship crews that reboarded their ships after Baker were higher than those for support ship crews. A summary of film badge readings (in roentgens) for July and August, when the largest number of personnel was involved, is listed below:
Actual film badge readings (R gamma)
| Readings | Total | 0 | 0.001 - 0.1 | 0.101 - 1.0 | 1.001 - 10.0 | July | 3,767 (100%) | 2,843 (75%) | 689 (18%) | 232 (6%) | 3 (<0.1%) | August | 6,664 (100%) | 3,947 (59%) | 2,139 (32%) | 570 (9%) | 8 (0.1%) |
Bikini after Crossroads
The 167 Bikini residents were moved to the uninhabited Rongerik Atoll prior to Crossroads, but were unable to feed themselves in the new environment. Visitors to Rongerik reported the islanders were facing potential starvation by January 1947, suffering malnutrition by July, and emaciated by January 1948. In March 1948 they were evacuated to Kwajalein Atoll, and then settled onto another uninhabited island, Kili, in November. With only one third of a square mile, Kili has one tenth the land area of Bikini and, more importantly, has no lagoon and no protected harbor. Unable to practice their native culture of lagoon fishing, they have been dependent on food shipments ever since. Their four thousand descendents today are living on several islands and in foreign countries.
Their desire to return to Bikini was thwarted indefinitely by the U.S. decision to resume nuclear testing at Bikini in 1954. During the spring and summer months of 1954, 1956, and 1958, twenty-one more nuclear bombs were detonated at Bikini, yielding a total of 75 megatons, equivalent to more than three thousand Baker bombs. Only one was a "self cleansing" air burst, the 3.8 megaton Redwing Cherokee test. The rest were surface bursts producing massive local fallout. The first was the dirtiest, the 15 megaton Bravo shot of Operation Castle on March 1, 1954, the largest ever U.S. test. Fallout from Bravo caused radiation injury to Bikini islanders who were living on Rongelap Atoll at the time.
The brief attempt to resettle Bikini from 1974 until 1978 was aborted when health problems from radioactivity in the food supply caused the atoll to be evacuated again. Sport divers who visit Bikini to dive on the shipwrecks must eat imported food. The lagoon is teeming with fish, but none of it is safe to eat.
Popular culture
The name "Bikini" was adopted for bikini swimwear shortly thereafter; a coincidence of explosive shock perhaps ("like the bomb, the bikini is small and devastating"), and the realization that "atom bombs reduce everybody to primitive costume."
The 1988 film Radio Bikini was nominated for the Best Documentary Feature Oscar. Directed by Robert Stone, it recounts the story of Operation Crossroads, concentrating on how it affected the Bikini islanders (they were deported en masse to Rongerik Atoll) and the servicemen who took part in the operation. The film almost exclusively uses archival footage, much of it in color. Video of the Crossroads Baker explosion is among the most often shown videos of a nuclear explosion, and exists in many sources.
See also
Special Delivery, a propaganda film made about the testing.
External links
- , made by U.S. Military combat artists, as a report of the tests.
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- showing Bikini Atoll and, particularly, the Castle Bravo crater.
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