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Operation Crossroads

Operation Crossroads
Mushroom-shaped cloud and water column from the underwater Baker nuclear explosion of July 25, 1946. Photo taken from a tower on Bikini Island, 3.5 miles (5.6 km) away.
Information
Country United States
Test site NE Lagoon, Bikini Atoll
Period 1946
Number of tests 2
Test type Free fall air drop, Underwater
Max. yield 23 kilotonnes of TNT (96 TJ)
Navigation
Previous test series Trinity
Next test series Sandstone

Operation Crossroads was a pair of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. They were the first nuclear weapon tests since Trinity in July 1945, and the first detonations of nuclear devices since the atomic bombing of Nagasaki on August 9, 1945. The purpose of the tests was to investigate the effect of nuclear weapons on warships.

The Crossroads tests 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. They were conducted by Joint Army/Navy Task Force One, headed by Vice Admiral William H. P. Blandy, rather than by the Manhattan Project, which had developed nuclear weapons during World War II. A fleet of 95 target ships was assembled in Bikini Lagoon and hit with two detonations of Fat Man plutonium implosion-type nuclear weapons of the kind dropped on Nagasaki, each with a yield of 23 kilotons of TNT (96 TJ).

The first test was Able. The bomb, named Gilda after Rita Hayworth's character in the 1946 eponymous film, was dropped from the B-29 Superfortress Dave's Dream of the 509th Bombardment Group on July 1, 1946, and detonated 520 feet (158 m) above the target fleet. It caused less than the expected amount of ship damage because it missed its aim point by 2,130 feet (649 m). The second test was Baker. The bomb, known as Helen of Bikini, was detonated 90 feet (27 m) underwater on July 25, 1946. Radioactive sea spray caused extensive contamination. A third deep water test, Charlie, planned for 1947, was canceled primarily because of the United States Navy's inability to decontaminate the target ships after the Baker test. Ultimately, only nine target ships were able to be scrapped rather than scuttled. Charlie was rescheduled as Operation Wigwam, a deep water shot conducted in 1955 off the California coast.

Bikini's native residents agreed to evacuate the island, with most moving to the Atomic Energy Commission, called Baker "the world's first nuclear disaster."[1]

Contents

  • Background 1
  • Opposition 2
  • Preparation 3
    • Ships 3.1
    • Cameras 3.2
    • Nicknames 3.3
  • Test Able 4
    • Able target array 4.1
    • Radiation 4.2
  • Test Baker 5
    • Baker target array 5.1
    • Sequence of blast events 5.2
    • Arkansas 5.3
    • Aircraft carriers 5.4
    • Fission-product radioactivity 5.5
    • Test animals 5.6
    • Induced radioactivity 5.7
    • Unfissioned plutonium 5.8
  • Failed Baker cleanup and program termination 6
    • Radiation monitoring 6.1
    • Cleanup issues 6.2
    • Secondary contamination 6.3
    • Warren persuades Blandy 6.4
  • Test Charlie 7
  • Operation Crossroads follow-up 8
  • Exposure of personnel 9
  • Bikini after Operation Crossroads 10
  • Legacy 11
  • Notes 12
  • References 13
  • Further reading 14
  • External links 15

Background

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."[2] With very few bombs available, he suggested a large number of targets 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.[3] The Strauss test would be designed to demonstrate ship survivability.[4]

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, Catron, Bracken, Burleson, Gilliam, Fallon, unknown ship, Fillmore, Kochab, Luna, and an unidentified tanker and liberty ship. On the right are LSM-203 and LSM-465. Farther in the background are a floating drydock and a merchant ship hulk.

Nine days later, Senator 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."[5] On September 19, the Chief of the United States Army Air Forces (USAAF), General of the Army Henry H. Arnold, asked the Navy to set aside ten of the thirty-eight captured Japanese ships for use in the test proposed by McMahon.[6]

Meanwhile, the Navy proceeded with its own plan, which was revealed at a press conference on October 27 by the Commander in Chief, United States Fleet, Fleet Admiral Ernest King. It involved between 80 and 100 target ships, most of them surplus U.S. ships.[6] 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.'"[7]

The Army's candidate to direct the tests, Major General Leslie Groves, head of the Manhattan Project which built the bombs, did not get the job. The Joint Chiefs of Staff decided that because the Navy was contributing the most men and materiel, the test should be headed by a naval officer. Commodore William S. "Deak" Parsons was a naval officer who had worked on the Manhattan Project and participated in the bombing of Hiroshima.[8] He was now the assistant to the Deputy Chief of Naval Operations for Special Weapons, Vice Admiral William H. P. Blandy,[9] whom he proposed for the role. This recommendation was accepted, and on January 11, 1946, President Harry S. Truman appointed Blandy as head of Army/Navy Joint Task Force One (JTF-1), which was created to conduct the tests. Parsons became Deputy Task Force Commander for Technical Direction. USAAF Major General William E. Kepner was Deputy Task Force Commander for Aviation. Blandy codenamed the tests Operation Crossroads.[10][11]

Under pressure from the Army, Blandy agreed to crowd more ships into the immediate target area than the Navy wanted, but he refused USAAF Major 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 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

Pressure to cancel Operation Crossroads altogether came from scientists and diplomats. Manhattan Project scientists 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 the scientists pointed out that the tests might demonstrate ship survivability while ignoring the effect of radiation on sailors,[16] Blandy responded by adding test animals to some of the ships, thereby generating protests from animal rights advocates.[17]

Secretary of State James F. Byrnes, who a year earlier had told physicist Leo Szilard that a public demonstration of the bomb might make the Soviet Union "more manageable" in Europe,[18] now argued the opposite: that further display of U.S. nuclear power could harden the Soviet Union's position against acceptance of the Acheson–Lilienthal Plan, which discussed possible methods for the international control of nuclear weapons and the avoidance of future nuclear warfare. 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 Congressmen complained about the destruction of $450 million worth of target ships, 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 the USS Texas, but the JTF-1 replied that "it is regretted that such ships as the USS 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 materiel. The test site had to be in territory controlled by the United States. The inhabitants would have to be evacuated, so it was best if it was uninhabited, or nearly so, and at least 300 miles (500 km) from the nearest city. So that a B-29 could drop a bomb, there had to be an airbase within 1,000 miles (1,600 km). To contain the target ships, it needed to have a protected anchorage at least 6 miles (10 km) wide. Ideally, it would have predictable weather patterns, and be free of severe cold and violent storms. Predictable winds would avoid having radioactive material blown back on the task force personnel, and predictable ocean currents would allow material to be kept away from shipping lanes, fishing areas, and inhabited shores.[23] Timing was critical because Navy manpower required to move the ships was being released from active duty as part of the post–World War II demobilization, and civilian scientists knowledgeable about atomic weapons were leaving federal employment for college teaching positions.[24]

On January 24, Blandy named the Bikini Lagoon as the site for the two 1946 detonations, Able and Baker. The deep underwater test, Charlie, scheduled for early 1947, would take place in the ocean west of Bikini.[25] Of the possible places given serious consideration, including Ecuador's Galápagos Islands, Bikini offered the most remote location with a large protected anchorage, suitable but not ideal weather,[26] 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. The Navy had been studying test sites since October 1945 and was ready to announce its choice of Bikini soon after Truman's declaration.[27] On February 6, the survey ship Sumner began blasting channels through the Bikini reef into the lagoon. The local residents were not told why.[28]

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." He also claimed it was "for the good of mankind and to end all world wars." 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."[29] On March 6, 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, LST 861 moved them and their belongings 128 miles (206 km) east to the uninhabited Rongerik Atoll, to begin a permanent exile.[30] 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.[31] As of 2015, the atoll remains unpopulated.[32]

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 short tons (90 t) of dynamite were used to remove coral heads from Bikini Lagoon. On the grounds of the David Taylor Model Basin outside Washington, DC, dress rehearsals for Baker were conducted with dynamite and model ships in a pond named "Little Bikini."[33] 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.[34] The arrangement also reflected the outcome of the Army/Navy disagreement about how many ships should be allowed to sink.[35]

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.[24] 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[36] were supplied by the 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.[24] Amphibious target ships were beached on Bikini Island.[37]

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 female nurses.[38] 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.[39] The islands of the Bikini Atoll were used as instrumentation sites and, until Baker contaminated them, as recreation sites.[40]

Cameras

Universal Newsreel about the first blast

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 could fly into radiation environments, such as Able's mushroom cloud, which would have been lethal to crew members.[41] 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 took 50,000 still pictures and 1,500,000 feet (460,000 m) of motion picture film. One of the cameras could shoot 1,000 frames per second.[42]

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 (19 km) east of the atoll. Test personnel were issued special dark glasses to protect their eyes, but a decision was made shortly before Able that the glasses might not be adequate. 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".[39]

Nicknames

Able and Baker are the first two letters of the Joint Army/Navy Phonetic Alphabet, used from 1941 until 1956. Alpha 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;[43] in the official JTF-1 history, the term M or Mike hour is used instead.[44]

The two bombs were Fat Man plutonium implosion-type nuclear weapons of the kind dropped on Nagasaki. The Able bomb was stenciled with the name Gilda and decorated with an Esquire magazine photograph of Rita Hayworth, star of the 1946 movie, Gilda.[45] 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.[46]

The plutonium core used in Able had been nicknamed the "Demon core" by scientists at Los Alamos after two criticality accidents in 1945 and 1946. In each instance it killed a scientist, Harry K. Daghlian, Jr. and Louis Slotin respectively.[46][47] There were only seven nuclear bombs in existence in July 1946.[48]

United States' Crossroads series explosions
Name Date, time (UTC) Location Elevation + height Delivery Purpose Device Yield References
Able June 30, 1946 21:00:01.0 NE Lagoon, Bikini Atoll 0 + 158 m (518 ft) Free fall air drop Weapon effect Mk III "Gilda" 23 kt [49][50][51][52][53]
Baker July 24, 1946 21:34:59.8 NE Lagoon, Bikini Atoll 0 - 27.5 m (90 ft) Underwater Weapon effect Mk III "Helen of Bikini" 23 kt [49][50][53]
Charlie
(canceled)
March 1, 1947 NE Lagoon, Bikini Atoll 0 - 50 m (160 ft) Underwater Weapon effect Mk III 23 kt [53]

The United States' test series summary table is here: United States' nuclear testing series.

Test Able

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

Nevada painted in high visibility red-orange for the atomic tests

At 9:00 on July 1, Gilda was dropped from the B-29 Superfortress Dave's Dream of the 509th Bombardment Group. The plane, formerly known as Big Stink, had been the photographic equipment aircraft on the Nagasaki mission in 1945. It had been renamed in honor of Dave Semple, a bombardier who was killed during a practice mission on March 7, 1946.[54] Gilda detonated 520 feet (158 m) above the target fleet, with a yield of 23 kilotons. Five ships were sunk.[24][34] Two attack transports sank immediately, two destroyers within hours, and one Japanese cruiser the following day.[55]

Some of the 114 press observers expressed disappointment at the effect on ships.[56] The New York Times reported, prematurely, that "only two were sunk, one capsized, and eighteen damaged."[57] 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."[58]

The main cause of less-than-expected ship damage was that the bomb missed its aim point by 710 yards (649 m).[59] 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. Various explanations were offered, including the bomb's known poor ballistic characteristics, but none was convincing. Images of the drop were inconclusive. The bomb sight was checked and found error free. Pumpkin bomb drops were conducted, but were accurate. Colonel Paul W. Tibbets believed that the miss was caused by a miscalculation by the crew. The mystery was never solved.[60][61] There were other factors that made Able less spectacular than expected. Observers were much farther away than at the Trinity test, and the high humidity absorbed much of the light and heat.[62]

The battleship USS Nevada had been designated as the aim point for Able and was painted red, with white gun barrels and gunwales, to make her 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 USS Gilliam, in much less crowded water.[63]

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 bullseye for the bomb was ship #32, the battleship USS Nevada, which was painted red to aid the bombardier. The bomb landed closer to ship #5, the attack transport USS Gilliam. All submarines were on the surface.

Location at which ships sank[64]
# Name Type Yards from zero
5 Gilliam Transport 50
9 Sakawa Japanese cruiser 420
4 Carlisle Transport 430
1 Anderson Destroyer 600
6 Lamson Destroyer 760
Serious damage
# Name Type Yards from zero
40 Skate Submarine 400
12 Yard oiler 520
28 Independence Aircraft 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 Aircraft carrier 2,265

In addition to the five ships that sank, fourteen were judged to have serious damage or worse, mostly 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 USS Lamson, which sank, was farther away than seven ships that stayed afloat. Lamson was broadside to the blast, taking the full impact on her port side, while the seven closer ships were anchored with their sterns toward the blast, somewhat protecting the most vulnerable part of the hull.[65]

The only large ship inside the 1,000-yard (914 m) radius which sustained moderate, rather than serious, damage was the sturdily built Japanese battleship Nagato, ship #7, whose stern-on orientation to the bomb gave her 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 her being sunk. The Able bomb missed its target, and the symbolic sinking came three weeks later, in the Baker shot.[66]

Serious damage to ship #10, the aircraft carrier Saratoga, more than 1 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,[67] 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.[68][69]

Radiation

Aerial view of the mushroom cloud.
Aerial view of the Able mushroom cloud rising from the lagoon with the Bikini Island visible in the background. The cloud carried the radioactive contaminants into the stratosphere.

As with Little Boy (Hiroshima) and Fat Man (Nagasaki), the Crossroads Able shot was an air burst. These were purposely detonated high enough in the air to prevent surface materials from being drawn into the fireball. The height-of-burst for the first nuclear explosion Trinity, in New Mexico on July 16, 1945, was 100 feet (30 m); the device was mounted on a tower. It made a crater 6 feet (1.8 m) deep and 500 feet (150 m) wide, and there was some local fallout. The test was conducted in secret, and the world at large learned nothing about the radioactive fallout at the time.[70] To be a true air burst with no local fallout, the Trinity height-of-burst needed to be 580 feet (180 m).[71] 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."[72] There was no significant local fallout from Able.[73]

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.[74]

There was 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. Neutron activation of materials in the ships was judged to be a minor problem by the standards of the time. One sailor on the support ship USS Haven 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.[75] Within a day nearly all the surviving target ships had been reboarded. The ship inspections, instrument recoveries, and moving and remooring of ships for the Baker test proceeded on schedule.[76]

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.[77] 35% of these animals died or were sacrificed in the three months following the explosion: 10% were killed by the air blast, 15% were killed by radiation, and 10% were killed by the researchers as part of later study.[78] The most famous survivor was Pig 311, which was found swimming in the lagoon after the blast and was brought back to the National Zoo in Washington, DC.[79]

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 demon core, victims who were close enough to receive a lethal dose died, while those farther away recovered and survived. Also, all the mice were placed outside the expected lethal zone in order to study possible mutations in future generations.[80]

Although the Able bomb missed its target, the Nevada, by nearly half a mile, and it failed to sink or to contaminate the battleship, a crew would not have survived. 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.[81] Had the Nevada been fully manned, she would likely have become a floating coffin, dead in the water for lack of a live crew. In theory, every unprotected location on the ship received 10,000 rems (100 Sv) of initial nuclear radiation from the fireball.[71] Therefore, people deep enough inside the ship to experience a 90% radiation reduction would still have received a lethal dose of 1,000 rems.[82] In the assessment of the 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."[16]

Test Baker

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

In Baker on July 25, 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 (55 m) deep. How/Mike Hour was 08:35.[24] No identifiable part of LSM-60 was ever found; it was presumably vaporized by the nuclear fireball. Ten ships were sunk,[83] 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.[84]

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. One picture shows a mark where the 27,000 ton battleship USS Arkansas was.[85]

As with Able, any ships that remained afloat within 1,000 yards (914 m) 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 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.[86]

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 (914 m) from the point of detonation, outlines the area of serious ship damage. The blue circle, 330 yards (302 m) 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: Pilotfish, ship #8, to a keel depth of 56 feet (17 m), Apogon, ship #2, to a keel depth of 100 feet (30 m), and Skipjack, ship #41, to 150 feet (46 m).

Ships sunk[64]
# Name Type Yards from surface zero
50 LSM-60 Amphibious 0
3 Arkansas Battleship 170
8 Pilotfish Submarine 363
10 Saratoga Aircraft 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

The German heavy cruiser Prinz Eugen, ship #36, 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.[87]

The submarine USS Skipjack was the only sunken ship successfully raised at Bikini.[88] She was towed to California and sunk again, as a target ship off the coast, two years later. [89]

Three other ships, all in sinking condition, were towed ashore at Bikini and beached:[90] attack transport USS Fallon, ship #25; destroyer USS Hughes, ship #27; and submarine USS Dentuda, ship #24. Dentuda, being submerged (thus avoiding the base surge) and outside the 1,000 yards (914 m) circle, escaped serious contamination and hull damage and was successfully decontaminated, repaired, and briefly returned to service.[91]

Sequence of blast events

The Baker shot produced so many unusual phenomena that a conference was held two months later to standardize nomenclature and define new terms for use in descriptions and analysis.[92] The underwater fireball took the form of a rapidly expanding hot gas bubble that 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 (1600 m/s), five times faster than that of sound in air.[93] 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.[94] Close behind the slick was a visually more dramatic, but less destructive whitening of the water surface called the "crack".[95]

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.[96] 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.[97]

During the first full second, the expanding bubble removed all the water within a 500-foot (152 m) radius and lifted two million tons[98] of spray and seabed sand into the air. As the bubble rose at 2,500 feet per second (762 m/s),[99] it stretched the spray dome into a hollow cylinder or chimney of spray called the "column," 6,000 feet (1,829 m) tall and 2,000 feet (610 m) wide, with walls 300 feet (91 m) thick.[100]

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.[100]

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.[101]

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