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Coordinates: 11°36′N 165°30′E / 11.6°N 165.5°E / 11.6; 165.5

Mushroom-shaped cloud and water column from the underwater nuclear explosion of July 25, 1946. Photo taken from a tower on Bikini Island, 3.5 mi (5.6 km) away.
The most famous Baker picture. The Wilson cloud has lifted revealing the fully formed spray column. The black area on the right of the column marks the position of the battleship Arkansas.

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:[1] Able was detonated at an altitude of 520 feet (158 m) on July 1, 1946; Baker was detonated 90 feet (27 m) underwater on July 25, 1946. A third burst, Charlie, planned for 1947, was canceled primarily because of the Navy's inability to decontaminate the target ships after the Baker test.

The Crossroads tests were the fourth and fifth nuclear explosions conducted by the United States (following the Trinity test and the bombings of Hiroshima and Nagasaki). They were the first of many nuclear tests held in the Marshall Islands, and the first to be publicly announced beforehand and observed by an invited audience, including a large press corps.

The most important result from Crossroads, though not widely reported at the time, was the radioactive contamination of all the target ships by the underwater Baker shot. It was the first case of immediate, concentrated local radioactive fallout from a nuclear explosion. (The fallout from an air burst is global, held in the stratosphere for days and widely dispersed.)[2] Chemist Glenn Seaborg, the longest-serving chairman of the Atomic Energy Commission, called Baker "the world's first nuclear disaster."[3]

To prepare the atoll for Crossroads, Bikini's native residents were evicted from their homes and resettled on smaller, uninhabited islands where they were unable to sustain themselves.[4] Later, in the 1950s, a series of large thermonuclear tests rendered Bikini unfit for subsistence farming and fishing. Because of radioactive contamination, Bikini remains uninhabited as of 2010, though it is occasionally visited by sport divers. Although participants in the Crossroads tests were well protected against acute radiation sickness, their life expectancy was reduced by about three months.[5]

Contents

Background

Aerial photo of target ships anchored in a row at Pearl Harbor, Hawaii.
Prospective Operation Crossroads target ships and support ships at Pearl Harbor on February 27, 1946. Ships from front to rear: USS Crittenden (APA-77), Catron (APA-71), Bracken (APA-64), Burleson (APA-67), Gilliam (APA-57), Fallon (APA-81), unknown ship, Fillmore (APA-83), Kochab (AKS-6), Luna (AKS-7) and an unidentified tanker and liberty ship. On the right are LSM-203 and LSM-465. Further in the background are a floating drydock and a merchant ship hulk.

The first proposal to test nuclear weapons against naval warships was made on August 16, 1945, by Lewis Strauss, future chairman of the Atomic Energy Commission. In an internal memo to Secretary of the Navy James Forrestal, Strauss argued, "If such a test is not made, there will be loose talk to the effect that the fleet is obsolete in the face of this new weapon and this will militate against appropriations to preserve a postwar Navy of the size now planned."[6] With very few bombs available, he suggested a large number of target ships widely dispersed over a large area. A quarter century earlier, in 1921, the Navy had suffered a public relations disaster when General Billy Mitchell's bombers sank every target ship the Navy provided for the Project B ship-versus-bomb tests. The Strauss test would be designed to demonstrate ship survivability, at least in theory; in the end, the entire target fleet would be effectively destroyed by radioactivity.

Nine days later, Senator Brien McMahon, who within a year would author the Atomic Energy Act and organize and chair the Congressional Joint Committee on Atomic Energy, made the first public proposal for such a test, but one designed to demonstrate the vulnerability, rather than survivability, of ships. He proposed dropping an atomic bomb on captured Japanese ships and suggested, "The resulting explosion should prove to us just how effective the atomic bomb is when used against the giant naval ships."[7] On September 19, Army Air Forces (AAF) Chief, Major General Henry H. Arnold, asked the Navy to save ten of the thirty-eight captured Japanese ships for use in the test proposed by McMahon.[8]

Meanwhile, the Navy proceeded with its own plan, revealed on October 27 by Admiral Ernest King at a press conference. It involved between 80 and 100 target ships, most of them surplus U.S. ships.[8] As the Army and the Navy maneuvered for control of the tests, Assistant Secretary of War Howard C. Peterson observed, "To the public, the test looms as one in which the future of the Navy is at stake,. .. if the Navy withstands [the tests] better than the public imagines it will, in the public mind the Navy will have 'won.'"[9]

The Navy won the contest to design and control the tests, and on January 11, 1946, Admiral William H. P. Blandy was appointed head of Army/Navy Joint Task Force One (JTF-1), newly created to conduct the tests which he named Operation Crossroads.[10] The Army's candidate to direct the tests, General Leslie Groves, head of the wartime Manhattan Project that built the bombs, did not get the job.[11]

Under pressure from the Army, Admiral Blandy agreed to crowd more ships into the immediate target area than the Navy wanted, but he refused AAF General Curtis LeMay's demand that, "every ship must have a full loading of oil, ammunition, and fuel."[12] Blandy's argument was that fires and internal explosions might sink ships that would otherwise remain afloat and be available for damage evaluation. When Blandy proposed an all-Navy board to evaluate the results, Senator McMahon complained to President Harry Truman that the Navy should not be "solely responsible for conducting operations which might well indeed determine its very existence."[13] Truman acknowledged that "reports were getting around that these tests were not going to be entirely on the level." He imposed a civilian review panel on Operation Crossroads to "convince the public it was objective."[14]

Opposition to the tests

Pressure to cancel Operation Crossroads altogether came from scientists and diplomats. Manhattan Project scientists who had argued for a public test of the bomb in lieu of dropping it on a Japanese city, now argued that further testing was unnecessary and environmentally dangerous. A Los Alamos study warned "the water near a recent surface explosion will be a witch's brew" of radioactivity.[15] When they complained that the tests might demonstrate ship survivability while ignoring the effect of radiation on sailors,[16] Admiral Blandy responded by adding test animals to some of the ships, which generated protests from animal rights advocates.[17]

Secretary of State James Byrnes, who a year earlier had told physicist Leo Szilard that a public demonstration of the bomb might make Russia "more manageable" in Europe,[18] now argued the opposite: that further display of U.S. nuclear power could harden Russia's position against acceptance of the Acheson-Lilienthal Plan. At a March 22 cabinet meeting he said, "from the standpoint of international relations it would be very helpful if the test could be postponed or never held at all." [19] He prevailed on Truman to postpone the first test for six weeks, from May 15 to July 1. For public consumption, the postponement was explained as an opportunity for more Congressional observers to attend during their summer recess.[20]

When Congressional critics complained about the destruction of $450 million worth of target ships, Admiral Blandy replied that their true cost was their scrap value at $10 per ton, only $3.7 million.[21] Veterans and legislators from New York and Pennsylvania requested to keep their namesake battleships as museum ships, as Texas had done with its battleship, but the JTF-1 replied, "... it is regretted that such ships as the New York cannot be spared."[22]

Preparation

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 (10 km) wide
  • A site which was uninhabited, or nearly so
  • A location at least 300 miles (480 km) from the nearest city
  • Weather patterns without severe cold and violent storms
  • Predictable winds directionally uniform from sea level to 60,000 feet (18,000 m)
  • 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.[1]

On January 24, Admiral Blandy named the Bikini Lagoon as the site for the two 1946 detonations, Able and Baker. The deep underwater test, Charlie scheduled for the spring of 1947, would take place in the ocean west of Bikini.[23] Of the possible places given serious consideration, including Ecuador's Galápagos Islands, Bikini offered the most remote location with a large protected anchorage, suitable weather,[24] and a small, easily-moved population. It had come under exclusive United States control on January 15, when Truman declared the United States to be the sole trustee of all the Pacific islands captured from Japan during the war.[25] On February 6, the survey ship Sumner began blasting channels through the Bikini reef into the lagoon. The local residents were not told why.[26]

The 167 Bikini islanders first learned their fate four days later, on Sunday, February 10, when Navy Commodore Ben H. Wyatt, United States military governor of the Marshall Islands, arrived by seaplane from Kwajalein. Referring to Biblical stories which they had learned from Protestant missionaries, he compared them to "the children of Israel whom the Lord saved from their enemy and led into the Promised Land." There was no signed agreement, but he reported by cable "their local chieftain, referred to as King Juda, arose and said that the natives of Bikini were very proud to be part of this wonderful undertaking."[27] On March 6, Commodore Wyatt attempted to stage a filmed reenactment of the February 10 meeting in which the Bikinians had given away their atoll. Despite repeated promptings and at least seven retakes, Juda confined his on-camera remarks to, "We are willing to go. Everything is in God's hands." The next day, a Navy LST moved them and their belongings 128 miles (206 km) east to the uninhabited Rongerik Atoll, to begin a so-far permanent exile.[28] 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. As of 2010, the atoll remains unpopulated.[29]

Map of Bikini Atoll, with target area highlighted.
All 167 native residents were moved 128 miles (206 km) east to the uninhabited Rongerik Atoll.

Ships

To make room for the target ships, 100 tons of dynamite were used to remove coral heads from Bikini Lagoon. On the grounds of the David Taylor Model Basin outside Washington, D.C., dress rehearsals for Baker were conducted with dynamite and model ships in a pond named "Little Bikini."[30]

A fleet of 95 target vessels was assembled in Bikini Lagoon. At the center of the target cluster, the density was 20 ships per square mile (7.7 per km²), three to five times greater than military doctrine would allow. The stated goal was not to duplicate a realistic anchorage, but to measure damage as a function of distance from the blast center, at as many different distances as possible.[31] The arrangement also reflected the outcome of the Army/Navy disagreement about how many ships should be allowed to sink.[32]

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.[1] The ships carried sample amounts of fuel and ammunition plus scientific instruments to measure air pressure, ship movement, and radiation. The live animals on some of the target ships[33] were supplied by support ship USS Burleson, which brought 200 pigs, 60 guinea pigs, 204 goats, 5,000 rats, 200 mice, and grains containing insects to be studied for genetic effects by the National Cancer Institute.[1] Amphibious target ships were berthed on Bikini Island.

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.[34] Additional personnel were located on nearby atolls such as Eniwetok and Kwajalein. Navy personnel were allowed to extend their service obligation for one year if they wanted to participate in the tests and see an atomic bomb explode.[35] 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.[36]

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 (457 km) of motion picture film. One of the cameras could shoot 1,000 frames per second.[37]

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".[35]

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;[38] in the official JTF-1 history, the term "M" or "Mike" hour is used instead.[39]

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 for a 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 (Harry K. Daghlian, Jr. and Louis Slotin).

Test Able – July 1

The airburst nuclear explosion of July 1, 1946. Photo taken from a tower on Bikini Island, 3.5 mi (5.6 km) away.
Crossroads Able, a 23-kiloton air-deployed nuclear weapon detonated on July 1, 1946. This bomb used, and consumed, the infamous Demon core that took the lives of two scientists in two separate criticality accidents.

At 0900[1] the weapon was dropped from the B-29 Superfortress Dave's Dream (formerly Big Stink of the 509th Composite Group) and detonated 520 feet (158 m) 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.

Some of the 114 press observers expressed disappointment at the effect on ships.[40] The New York Times reported, prematurely, that "only two were sunk, one capsized, and eighteen damaged."[41] 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."[42]

However, the main cause of less-than-expected ship carnage was that the bomb missed its aim point by 710 yards (649 m).[43] 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 (366 m) 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

Map showing ship locations for the nuclear explosion of July 1, 1946. The locations of the 19 ships listed in the accompanying tables are marked with symbols and numbers.
The array of target ships in Bikini lagoon for the Able shot of Operation Crossroads. Half of the target ships were outside the area of this map. The five red X's mark the five ships that sank. The tables (right) contain the key to ship numbers. The circle, with a radius of 1,000 yards (914 m) from the point of detonation, outlines the area of serious ship damage. The intended bulls-eye for the bomb was ship #32, the battleship Nevada, which was painted red to aid the bombardier. The bomb landed closer to ship #5, the attack transport Gilliam. All submarines were on the surface.
Ships sunk[44] – 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
Serious damage – Yards from zero
# Name Type Distance
40 Skate Submarine 400
12 YO-160 Yard Oiler 520
28 Independence A/C Carrier 560
22 Crittenden Transport 595
32 Nevada Battleship 615
3 Arkansas Battleship 620
35 Pensacola Cruiser 710
11 ARDC-13 Drydock 825
23 Dawson Transport 855
38 Salt Lake City Cruiser 895
27 Hughes Destroyer 920
37 Rhind Destroyer 1,012
49 LST-52 LST 1,530
10 Saratoga A/C Carrier 2,265

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 (914 m) 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 (1.6 km) from the blast, was due to fire. For test purposes, all the ships carried sample amounts of fuel and ordnance, plus airplanes. Most warships carried a seaplane on deck, which could be lowered into the water by crane,[45] but the Saratoga carried several airplanes with highly volatile aviation fuel, both on deck and in the hangars 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 2 miles (3.2 km) wide.[46] But water doesn't burn, and warships, other than aircraft carriers, are extremely resistant to blast and fire.

Radiation

Two goats penned on ship deck, within reach of water and food.
Test animals were deliberately confined to the ships of Operation Crossroads. Goat #53, penned like this on the Nevada deck, died of radiation exposure two days after Able.[47]

As with all three previous nuclear detonations – Trinity, Little Boy (Hiroshima), and Fat Man (Nagasaki) – the Crossroads Able shot was an air burst,[2] 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."[48] 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).[49] Within a day nearly all the surviving target ships had been reboarded. The ship inspections, instrument recoveries, and moving and remooring ships for the Baker test proceeded on schedule.

Fifty-seven guinea pigs, 109 mice, 146 pigs, 176 goats, and 3,030 white rats had been placed on 22 target ships in stations normally occupied by people.[50] 10% of the animals were killed by the air blast, 15% were killed by fireball radiation, and 10% were killed during later study. Altogether, 35% of the animals died as a direct result of blast or radiation exposure.[51]

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, and only 65% of the animals survived, some of the rats were killed.[52]

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 (having survived two days longer than goat #53 which was on the deck, unshielded).[53] Had the Nevada been fully manned, she would likely have become a floating coffin, dead in the water for lack of a live crew.[54]

Test Baker – July 25

Watercolor of geyser lifting one end of a ship.
"Battleship Arkansas Being Tossed in Giant Pillar," watercolor by Grant Powers, U.S.M.C, 1946

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.[1] No identifiable part of LSM-60 was ever found; it was presumably vaporized by the nuclear fireball. Ten ships were sunk, including the German heavy cruiser Prinz Eugen 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 a mark where the 27,000 ton battleship Arkansas was.[55]

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. Regardless of the degree of damage, only nine surviving Baker target ships were eventually decontaminated and sold for scrap. The rest were sunk at sea after decontamination efforts failed.[56]

Baker target array

Map showing ship locations for the nuclear explosion of July 25, 1946. The locations of the 10 ships listed in the accompanying table are marked with symbols and numbers.
The array of target ships in Bikini lagoon for the Baker shot of Operation Crossroads. Half of the target ships were outside the area of this map. The ten red X's mark the ten ships that sank. The table (left) contains the key to ship numbers. The black circle, with a radius of 1,000 yards from the point of detonation, outlines the area of serious ship damage. The blue circle, 330-yard radius, marks the rim of the shallow underwater crater created by the blast, as well as the outer circumference of the hollow water column which enveloped the Arkansas. The submarines were submerged, the Pilotfish, ship #8, to a keel depth of 56 feet, and the Apogon, ship # 2, to a keel depth of 100 feet.
Ships sunk[44] – 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 December 22, 1946, five months after Baker. She remains there today, with starboard propeller blades in the air.[57]

The submarine Skipjack was the only sunken ship successfully raised at Bikini.[58] 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:[59] 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.[60]

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.[61] 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.[62] Close behind the slick was a visually more dramatic, but less destructive whitening of the water surface called the "crack."[63]

When the gas bubble's diameter equaled the water depth, 180 feet (55 m), it hit the sea floor and the sea surface simultaneously. At the bottom, it started digging a shallow crater, ultimately 30 feet (9 m) deep and 2,000 feet (610 m) wide.[64] 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.[65]

During the first full second, the expanding bubble removed all the water within a 500-foot (152 m) radius and lifted two million tons[66] of spray and seabed sand into the air. As the bubble rose at 2,500 feet per second (762 m/s),[67] it stretched the spray dome into a hollow cylinder or chimney of spray called the "column," 6,000 feet (1,829 m) tall, 2,000 feet (610 m) wide, and with walls 300 feet (91 m) 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.

Aerial photo of nuclear explosion rising from lagoon. Hemispherical condensation cloud on the surface is 1 mi (1.6 km) in diameter. In comparison, navy ships in the foreground look like bathtub toys.
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. 
The same scene five seconds later, photographed from a camera tower, showing a water column 2,000 ft (610 m) in diameter and 6,000 ft (1830 m) tall.
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 (305 m) from surface zero and 94 feet high.[68] By the time it reached the Bikini Island beach, 3.5 miles (6 km) away, it was a nine-wave set with shore breakers up to 15 feet (5 m) high, which tossed landing craft onto the beach and filled them with sand.[69]

Twelve seconds after detonation, falling water from the column started to create a 900-foot (274 m) 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.[68]

Battleship Arkansas

Arkansas was the closest ship to the bomb other than the ship from which it was suspended. 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;[70] 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.[55] 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.[71]

All large naval gunships are top heavy and settle upside down when they sink, a notable exception being the Bismarck, which sank upside down but righted itself after its turrets fell out on the way to the bottom. The Arkansas settled upside down, but a 1989 diver's sketch of the wreck[72] 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.[73]

Line drawing of partially-crushed battleship hull lying upside down on the seabed.
Battleship Arkansas upside down, 180 feet deep in Bikini Lagoon. Diver's sketch from a 1989 National Park Service dive. 
Underwater photograph of a gun protruding from an opening in the side of a sunken ship.
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. 
A permanently docked museum ship with a red circle on the photograph to highlight a gun protruding from an opening the in the ship's port side.
A similar battleship, Texas, with aircastle circled. At Bikini, everything that was above the lower deck guns of Arkansas 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.[74] 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.[75] She settled upright on the bottom, with the top of her mast 40 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.[76] (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.)[77]

Independence survived Able with spectacular damage to the flight deck.[78] 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.

Line drawing of aircraft carrier sitting upright on the seabed.
Diver's sketch of Saratoga on the bottom of Bikini Lagoon. Starboard torpedo blister is crumpled.
Photograph of badly damaged aircraft carrier, afloat with smoke coming from deck.
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.[2] 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.[79]

The Baker explosion produced about two pounds of fission products,[80] equivalent in radioactivity to hundreds of tons of radium.[81] 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.[82] 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.[83]

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.[84] Because of this constraint, only the five most distant target ships could be boarded on the first day.[85] 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.[86] 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.[87]

In the first six days after Baker, when radiation levels were highest, 4,900 men boarded target ships.[88] Sailors tried to scrub off the radioactivity with brushes, water, soap, and lye. Nothing worked, short of sandblasting to bare metal.[86]

Ships silhouetted against an approaching cloud of mist from falling water in the background.
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
Aerial photo of a fireboat hosing down the stern of a battleship.
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 of the above map. 
Sailors scrubbing down a ship deck.
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.[89] 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 takes on intense, short-term radioactivity 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 thousandfold, but the flip side of short half-life is high intensity at the beginning.)[90]

A small fraction of one pound of radioactive sodium was produced,[91] 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.[92]

Finally, the 11.6 pounds of plutonium which did not undergo fission[93] 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.[92]

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.[94]

Test Charlie

Charlie was to explode deep under the surface in the lee of the atoll to test effects on unmoored ships.[35] Charlie, originally scheduled for the spring on 1947, 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.[1] 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 follow-up

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.[33]

Radioactive parts of a fish show as white against a black background.
Lagoon contamination. A radioactive puffy surgeon fish makes its own X-ray. Bright area is a meal of fresh algae. The rest of the body has absorbed and distributed enough fission product radioactivity to make the entire fish radioactive. The fish was alive and apparently healthy when captured.

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.[95]

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.[96] 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.[97]

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."[98]

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."[99]

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."[100] 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.[101] 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."[102] 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 designed 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. Since there was no special clothing or radiation shielding available, the protection plan relied on managing who went where, when, and for how long.[33]

Radioactively "hot" areas were predicted in advance, and then checked with Geiger counters, sometimes by remote control, to see if they were safe. The level of measured gamma radiation determined how long personnel could operate there without exceeding the daily allowable dose.[33]

Instant gamma readings were taken by radiation safety specialists, but film-badge dosimeters, which could be read at the end of the day, were issued to all personnel believed to be at the greatest radiological risk. Anyone whose badge showed more than 0.1 R / day exposure was removed for one or more days from areas and activities of possible exposure. The maximum accumulated exposure recorded was 3.72 R, received by a radiation safety specialist.[33]

A percentage of each group working in less contaminated areas was badged. Eventually, 18,875 film-badge dosimeters were issued to about 15% of the total work force. On the basis of this sampling, a theoretical total exposure was calculated for each person who did not have a personal badge.[33] As expected, exposures for target ship crews that reboarded their ships after Baker were higher than those for support ship crews. However, the hulls of support ships that entered the lagoon after Baker became so hot that sleeping quarters were moved toward the center of each ship.[103]

Of the total mass of radioactive particles scattered by each explosion, 85% was unfissioned plutonium which produces alpha radiation not detected by film badges or Geiger counters. There was no method of detecting plutonium in a timely fashion, and participants were not monitored for ingestion of it.[92]

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[33] 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%)

In 1996, a government-sponsored mortality study of Crossroads veterans[104] showed that, by 1992, 46 years after the tests, veterans had experienced a 4.6% higher mortality than a control group of non-veterans. There were 200 more deaths among Crossroads veterans than in the similar control group (12,520 vs. 12,320), implying a life-span reduction of about three months for Crossroads veterans.[105] For the main expected causes of this increased mortality, leukemia and other cancers, the incidence was not significantly higher than normal. Death by those diseases was tabulated on the assumption that if radiation exposure had a life-shortening effect it was likely show up there, which it did not. There were not enough data gathered on other causes of death to determine the reason for this increase in all-cause mortality, and it remains a mystery. The mortality increase was higher, 5.7%, for those who boarded target ships after the tests than for those who did not, whose mortality increase was only 4.3%.[104]

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.[29]

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.[106] 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.[107]

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.

Legacy

Following test Baker decontamination problems, the United States Navy equipped newly constructed ships with a CounterMeasure WashDown System (CMWDS) of piping and nozzles to cover exterior surfaces of the ship with a spray of salt water from the firefighting system when nuclear attack appeared imminent. The film of flowing water would theoretically prevent contaminants from settling into cracks and crevices.[108]

The name "Bikini" was adopted for bikini swimwear during Operation Crossroads; 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."[109]

The 1976 Bruce Conner film Crossroads utilizes research footage coupled with a Terry Riley soundtrack.

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

References

  1. ^ a b c d e f g Daly 1986. Note: the bomb yields are often reported as 21 kilotons, but the figure of 23 kilotons is used consistently throughout this article.
  2. ^ a b c The height-of-burst for the first nuclear explosion Trinity, in New Mexico on July 16, 1945, was 100 feet; the device was atop a tower. It made a crater 6 feet deep and 500 feet wide, and there was some local fallout, Hansen 1995, p. 154, Vol 8, Table A-1. and Glasstone & Dolan 1977, pp. 409, 622. To be a true air burst with no local fallout, the Trinity height-of-burst needed to be 580 feet, Fletcher 1977. However, the test was conducted in secret, and the world at large learned nothing about radioactive fallout at the time.
  3. ^ Weisgall 1994, p. ix.
  4. ^ See: "Bikini after Crossroads" section in this article.
  5. ^ See: "Exposure to personnel" section in this article.
  6. ^ Strauss 1962, pp. 208,9.
  7. ^ Shurcliff 1947, p. 10.
  8. ^ a b Weisgall 1994, p. 16.
  9. ^ Peterson 1946, quoted in Weisgall 1994, p. 17.
  10. ^ Weisgall 1994, p. 31.
  11. ^ Weisgall 1994, p. 30.
  12. ^ Weisgall 1994, p. 126.
  13. ^ Weisgall 1994, p. 67.
  14. ^ Weisgall 1994, pp. 68,69.
  15. ^ Newson 1945, p. 4, quoted in Weisgall 1994, p. 216.
  16. ^ Bulletin Editors 1946, p. 1.
  17. ^ Delgado 1991, p. Ch 2.
  18. ^ Szilard 1978, p. 184.
  19. ^ Weisgall 1994, p. 90.
  20. ^ Weisgall 1994, p. 94. Despite the postponement, only 13 members of Congress witnessed the Able test, and 7 witnessed the Baker test. Shurcliff 1947, p. 185.
  21. ^ Weisgall 1994, p. 79.
  22. ^ Letter, Brig. Gen. T. J. Betts, USA, to Peter Brambir, March 21, 1946, filed in Protest Answers, National Archives Record Group 374. Cited in Delgado 1991, p. Ch 2.
  23. ^ Weisgall 1994, p. 117.
  24. ^ Bikini failed to meet one of the stipulated weather criteria: "predictable winds directionally uniform from sea level to 60,000 feet." Daly 1986, p. 68. Like most tropical ocean locations, its surface winds blow westward and its stratospheric winds blow eastward.
  25. ^ The Navy had been studying test sites since October 1945 and was ready to announce its choice of Bikini soon after Truman's declaration of U.S. control over it. Weisgall 1994, pp. 31-33.
  26. ^ Weisgall 1994, pp. 105, 106.
  27. ^ Weisgall 1994, p. 107.
  28. ^ Weisgall 1994, p. 113.
  29. ^ a b Niedenthal 2008.
  30. ^ Shurcliff 1946, pp. 22, 23, 26, 27.
  31. ^ Shurcliff 1946, p. 119.
  32. ^ Weisgall 1994, p. 124.
  33. ^ a b c d e f g Navy History and Heritage Command 2002.
  34. ^ Shurcliff 1947, p. 33.
  35. ^ a b c Waters 1986, pp. 72-74.
  36. ^ Shurcliff 1946, p. 111.
  37. ^ Shurcliff 1946, p. 9.
  38. ^ Cunningham 1946, and Bradley 1948, pp. 40, 91.
  39. ^ Schurcliff 1947, pp. 109, 155.
  40. ^ Delgado 1991, p. 26.
  41. ^ New York Times, July 1, 1946, p 1.
  42. ^ New York Times, July 2, 1946, p 3.
  43. ^ Delgado 1991, p. 86.
  44. ^ a b Data in the table and the map come from Delgado 1991. The Able map is on p 16, the Baker map on p 17, and ship damage and distances on pp 86–136. The full text of this reference is posted on the Internet (see link in Sources, below).
  45. ^ Shurcliff 1946, pp. 165, 166, 168.
  46. ^ Fletcher 1977. For an explanation of the 5 psi lethal area, see Little Boy – Physical effects of the bomb.
  47. ^ Life Editors 1947, p. 77. These two goats, on the attack transport Niagara, may have been far enough away to survive. Delgado 1991, p. 22.
  48. ^ Shurcliff 1946, p. 143.
  49. ^ One sailor on the support ship USS Haven (AH-12) was found to be "sleeping in a shower of gamma rays" from an illegal metal souvenir he had taken from a target ship. Fireball neutrons had made it radioactive. Bradley 1948, p. 70.
  50. ^ Shurcliff 1946, p. 108.
  51. ^ Shurcliff 1947, p. 140.
  52. ^ Shurcliff 1947, pp. 140–144.
  53. ^ Life Editors 1947, p. 76.
  54. ^ In theory, every unprotected location on the ship received 10,000 rems of initial nuclear radiation from the fireball. Fletcher 1977. Therefore, people deep enough inside the ship to experience a 90% radiation reduction would still have received a lethal dose of 1,000 rems. Glasstone & Dolan 1977, p. 580. From Bulletin of the Atomic Scientists: "... a large ship, about a mile away from the explosion, would escape sinking, but the crew would be killed by the deadly burst of radiations from the bomb, and only a ghost ship would remain, floating unattended in the vast waters of the ocean." Bulletin Editors 1946, p. 1.
  55. ^ a b The upending was reported by Crossroads participants and depicted in two contemporary drawings (see Battleship Arkansas Being Tossed in Giant Pillar), but two authors have suggested that what looks like the silhouette of a vertical battleship hull is actually a gap in the water column, an upside-down rain shadow, caused by the unseen, still-horizontal hull of the Arkansas as it blocks the rise of water in the column. This explanation was given by Armiral Blandy, as reported in Weisgall 1994, pp. 163-164 (illustrations), and it was described as a possibility in Shurcliff 1947, pp. 155,156. Delgado stated it as a certainty in Delgado 1991, pp. 55,88, and again in Delgado 1996, p. 75. Delgado based his conclusion on frame-by-frame examination of motion picture film.
  56. ^ The fate of 13 small landing craft is unknown; they may have been sold for scrap, rather than scuttled. Delgado 1991, p. 33.
  57. ^ Delgado 1991, p. 60-64. In 1978, her port propeller was salvaged and is preserved at the German Naval Memorial at Laboe.
  58. ^ Delgado 1996, p. 83.
  59. ^ Delgado 1996, p. 87.
  60. ^ Shurcliff 1947, p. 151.
  61. ^ Glasstone & Dolan 1977, p. 244.
  62. ^ Glasstone & Dolan 1977, p. 48.
  63. ^ Glasstone & Dolan 1977, p. 49.
  64. ^ Glasstone & Dolan 1977, p. 251.
  65. ^ Glasstone & Dolan 1977, pp. 49, 50.
  66. ^ Shurcliff 1947, p. 156.
  67. ^ Glasstone & Dolan 1977, p. 50.
  68. ^ a b Glasstone & Dolan 1977, p. 52.
  69. ^ Shurcliff 1947, p. plate 29.
  70. ^ Shurcliff 1946, p. 151.
  71. ^ Delgado 1996, pp. 119, 120.
  72. ^ Delgado 1991, p. 95.
  73. ^ Delgado 1996, p. 117.
  74. ^ Delgado 1991, p. 101.
  75. ^ Shurcliff 1946, p. 213.
  76. ^ Davis 1994.
  77. ^ Niedenthal 2008 Letter posted August 23, 2008, by Jack Niedenthal, Tourism Operations Manager for the Bikini Atoll Local Government.
  78. ^ Shurcliff 1946, pp. 154-157.
  79. ^ Memorandum, Col. A. W. Betts, USACOE, to Brig. Gen. K. D. Nichols, MED, USACOE, August 10, 1946, quoted in Delgado 1996, p. 87.
  80. ^ The conversion ratio of fission to energy is two pounds of fission per 12 kilotons of energy. The 23-kiloton yield of the Baker device indicates that just under two pounds of plutonium-239 became fission products. Glasstone 1967, p. 481.
  81. ^ Shurcliff 1947, pp. 167, 168, & plate 28.
  82. ^ Shurcliff 1947, p. 159.
  83. ^ Glasstone & Dolan 1977, pp. 53-55.
  84. ^ Delgado 1996, p. 85.
  85. ^ Delgado 1991, p. 28.
  86. ^ a b Delgado 1991, p. 29.
  87. ^ Schurcliff 1947, p. 168.
  88. ^ Delgado 1996, p. 175.
  89. ^ A plutonium fission event produces, on average, 2.9 neutrons, most of which are consumed in the production of more fission, until fission stops and the remaining uncaptured neutrons escape. Glasstone 1967, p. 486.
  90. ^ Other radioisotopes were produced from seawater: hydrogen-3 from hydrogen-2, carbon-14 from oxygen-17, and chlorine-36 from chlorine-35, but due to low abundance and/or low short-term intensity (long half-life) they were considered insignificant compared with sodium-24. Delgado 1996, p. 86.
  91. ^ If all the neutrons released by the fission of two pounds of plutonium-239 were captured by sodium-23, 0.4 pounds of sodium-24 would result, but sodium did not capture all the neutrons.
  92. ^ a b c Delgado 1996, p. 86.
  93. ^ The total amount of plutonium in the core, later called the pit, was 13.6 pounds, two pounds of which fissioned. Coster-Mullen 2003, p. 45.
  94. ^ Schurcliff 1947, pp. 166–167.
  95. ^ Bradley 1948, pp. 105-105.
  96. ^ Delgado 1991, p. 31.
  97. ^ Delgado 1991, pp. 32, 33.
  98. ^ Delgado 1991, p. 33.
  99. ^ Director of Ship Material, JTF-1, "Technical Inspection Report, Radiological Inspection of Target and Non-Target Vessels," Armed Forces Special Weapons Project, 1947, National Archives, quoted in Delgado 1996, p. 86.
  100. ^ Life Editors 1947, p. 75.
  101. ^ Delgado 1996, p. 173.
  102. ^ Bradley 1948, p. xii.
  103. ^ Interview with Rear Admiral Robert Conard, MC, USNR (Ret.) in Setauket, NY, November 9, 1993, conducted by Jan K. Herman, Historian, Bureau of Medicine and Surgery "Interview". Department of the Navy -- Naval Historical Center. 2002-08-11. http://www.history.navy.mil/faqs/faq87-6b.htm. Retrieved 2009-09-27. 
  104. ^ a b Institute of Medicine 1996
  105. ^ The study did not publish life-span figures, but actuarial tables predict about 800 deaths per year for a group that size as they approach 70 years in age. Two hundred extra deaths would put the Crossroads veterans about three months ahead of their peers on the mortality curve. Social Security Online, Actuarial Publications, Period Life Table "Table". www.socialsecurity.gov. 2009-04-22. http://www.ssa.gov/OACT/STATS/table4c6.html. Retrieved 2009-11-10. 
  106. ^ Hansen 1995, p. 154, Vol 8, Table A-1.
  107. ^ Delgado 1996, p. 176.
  108. ^ "United States Navy CMWDS". http://www.dcfp.navy.mil/cbrd/decon/shipcmwds.htm. Retrieved 2009-12-17. 
  109. ^ Judson Rosebush, "Michele Bernadini: The First Bikini". Bikini Science. http://www.bikiniscience.com/chronology/1945-1950_SS/LR4601_S/LR4601.html. Retrieved 2007-09-19. 

Sources

External links








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