Operation Crossroads was a two shot nuclear testing series conducted in the summer of 1946. Crossroads was the first post-World War 2 nuclear testing series conducted by the United States, and the first nuclear weapons effects tests ever conducted. The atomic bombings of Hiroshima and Nagasaki provided an opportunity to study the effects of a nuclear explosion on a city, however, the effects of a nuclear explosion on ships were still unknown. For this reason, the series sought to study the effects of a nuclear explosion upon naval ships of various sizes and other military and civilian equipment.
Crossroads was seen as a means to measure the effectiveness of current naval power against atomic weapons, and determine if the development of nuclear weapons rendered the U.S. Navy obsolete. The nuclear tests sought answers to many questions, including to what amount and type of damage would the bombs produce in the first instance, to what extent should accepted principles of ship design be altered in future construction, what defensive measures could be taken by a ship attacked with atomic weapons, and whether traditional tactical practices were outdated. Operation Crossroads was the idea of Lewis Strauss, an aide to Secretary of Navy James Forrestal, and later Chairman of the U.S. Atomic Energy Commission. Early in 1944 the Manhattan Engineer District had given serious consideration to the possibility of testing an atomic bomb against the Japanese Navy at Truk Island. After the surrender of Japan, Senator Brien McMahon of Connecticut made a speech to the Senate in which he advocated the use of an atomic bomb against the captured Japanese fleet. Eventually, it was decided to use obsolete U.S., as well as captured Japanese and German vessels, for the Crossroads experiments. Presidential approval was given on 10 January 1945 to create Joint Task Force One (JTF 1). The purpose of JTF 1 was to organize and conduct nuclear tests in the Pacific during Operation Crossroads. Vice Admiral W.H.P Blandy was designated as Commander of JTF 1 (CJTF 1). Long distinguished in the field of ordnance engineering, and Chief of the Bureau of Ordnance from 1941 to 1943, Admiral Blandy saw action in the Pacific, was latterly Deputy Chief of Naval Operations, Special Weapons. Over 200 ships, 42,000 men, and 150 aircraft comprised the Task Force and included members of the Navy, Army Air and Ground Forces, and civilian scientists. Crossroads was publicly announced in December 1945. Vice Admiral Blandy gave an outline of the planned operation to the Special Committee on Atomic Energy. Over $70 million dollars would be spent for Operation Crossroads.
At least two tests were required, though as many as three or four were originally planned. One test would be conducted in the atmosphere, several hundred feet above a target array of over 70 ships. This test, code named Able, would study the response of various ships, equipment, and material against the effects of blast, thermal radiation, and radioactivity. A second test, code named Baker, would be fired underwater, with the ships of the target array at various distances from the epicenter. Baker sought to study the same effects as those studied for the Able shot. A third test, code named Charlie, would also be fired underwater but at a greater depth than Baker shot.
Over 90 target vessels would comprise the target array which would be exposed to the nuclear shots. These ships ranged in size from small, amphibious craft to aircraft carriers and battleships. Several plans for the arrangement of the target fleet were considered and revised. The directive creating Operation Crossroads specified a disposition of ships to give a graduation of damage from maximum to minimum. Major damage to ships close to the explosion point, minor damage to ships at the outskirts of the target circle, would provide valuable means of analyzing the bomb’s destructive force. Ships within the 500 yard radius around ground zero would be secured by fixed moorings fore and aft to prevent swinging. For Able, these ships included the heavy cruiser USS Pensacola, destroyer USS Hughes, Japanese battleship Nagato, light carrier USS Independence, submarine USS Skate, district craft YO-160, Japanese light cruiser Sakawa. Ships outside the 500 yard radius were anchored free to swing. Vessels anchored between the 1,000 yard and 4,000 yard boundary were disposed in a spoke like pattern around ground zero. These included rows of LSTs, LCTS, LCIs, two rows of transports, and one row of destroyers. The concentration of ships from a Navy standpoint was artificial. More than 20 ships were compressed within 1,000 years of ground zero. Ordinarily such an area would be used to contain but a single capital ship in a carrier force at sea, or three capital ships in a normal anchorage. The principle of using an arrangement that would provide graduated damage, instead of one representing a tactical formation or anchorage, was followed in both tests.
The tests, originally scheduled for May 15, 1946, were postponed six weeks by President Truman, to July 1, in order that members of Congress would be able to observe the shots. This delay gave more time for planning and preparations.
Bikini Atoll was chosen as the location for the nuclear tests to be fired during Operation Crossroads. The atoll is situated in the Marshall Islands group, in the western Pacific Ocean, some 2,000 miles southwest of Hawaii and 4,150 miles from San Fransisco. Discovered in 1526 by a Spanish sea captain, the islands were rediscovered and named by the English captains Gilbert and Marshall in 1788. After World War I the islands became a Japanese mandate. Throughout World War 2, Bikini Atoll served as an outpost for the Japanese headquarters in the Marshall Islands, Kwajalein Atoll.
The total land area of Bikini Atoll is 3.4 square miles, with Bikini and Eneu Islands compromising 586 acres and 308 acres, respectively. The total lagoon area is 240 square miles. Air temperature is 80-85 degrees all year. The months of June through December are wetter though with milder winds. The months of January through May are drier but with more wind; water temperature is 80-85 degrees all year. Food crops grown on Bikini include coconuts, pandanus, papaya, banana, arrowroot, taro, limes, breadfruit, and pumpkin. Animal life on Bikini and throughout the Marshalls includes small lizards, hermit crabs, coconut crabs, and a wide variety of birds. Pigs, ducks and chickens are raised for food, and dogs and cats are kept as pets. Several reasons motivated the decision to locate Operation Crossroads at Bikini. The atoll had an ideal size for the operation, average water depth inside the lagoon was approximately 200 feet and provided good anchorage for the target fleet. Bikini is located some 250 miles north of Kwajalein, a suitable base from which the bombing plane could operate. The atoll is remote from fishing and steamer lanes and has excellent weather conditions. 167 native Bikinians were living on the atoll at the time preparations for the Crossroads were being made. In February 1946, Commodore Ben H. Wyatt, the military governor of the Marshall Islands, traveled to Bikini to meet with the natives and discuss their relocation for the nuclear tests. On a Sunday, after church service, he Bikinians were assembled and asked to be temporarily relocated for Operation Crossroads. King Juda, the leader of the Bikinians, deliberated with his people for some time and stood before the American delegation and announced his people would leave the atoll for the tests.
The Bikini church and community house were dismantled and transported to Rongerik. Pandanus thatching for the new village on Rongerik was prefabricated. New housing was constructed by U.S. Personnel and the natives. Nine 8x8x5 foot concrete cisterns for catching rainwater were built. A total of 23,000 gallons of fresh water was put ashore at Rongerik to tide the village until the beginning of the rainy season. The U.S. Navy gave the natives a radio, powered by a small generator, from which they could listen to regular noonday broadcasts from Station WXLG on Kwajalein. Rongerik affairs were watched over by military government officials under the Kwajalein Island Commander. Life for the Bikinians on Rongerik deteriorated rapidly however. The islands of Rongerik Atoll were uninhabited because the Marshallese people considered them to be unlivable due to their size; Rongerik atoll is about 1/6 the size of Bikini Atoll. There was also a deep rooted traditional belief that the atoll was inhabited by evil spirits, called the Demon Girls of Ujae. Food supplies, good for several weeks, were left for the natives, but they soon discovered that the coconut trees and other local food crops produced very few fruits when compared to the yield of the trees on Bikini. The fish in the Rongerik lagoon were found to be uneatable. Within two months of their arrival on Rongerik, the natives began to beg US officials to move them back to Bikini.
Planning for Operation Crossroads went forward during the spring and early summer of 1946. Surveys of the Bikini lagoon were made and its waters combed for old Japanese mines. The surveys also charted the location of coral heads, which presented distinct obstructions for navigation and anchorage of the fleet. It was also necessary to remove coral from the lagoon floor for accurate studies of underwater shock waves produced by the nuclear explosions. These coral heads were blasted with explosives at Bikini from the lagoon floor. Over 100 tons of dynamite was used for coral head removal. The islands were sprayed with DDT to insure healthful conditions for the Task Force personnel. The airfield at Kwajalein was made ready for the arrival of the Air Group. Laboratories for chemical analysis and photograph processing were constructed. Kwajalein Atoll played a significant part in Operation Crossroads. For the purposes of the operation new asphalt plane parking areas were prepared, special fire-fighting systems were installed along the runway and special facilities were constructed for servicing the atomic bomb. The airstrip on Kwajalein also served as the main base for “Dave's Dream”, the aircraft selected to deliver the atomic bomb. At Kwajalein, during an important period in the peperationtory phase of Operation Crossroads, electric power on the island, normally supplied by two 250-kilotwatt generators, suddenly failed with no possibility of repair until special parts had been obtained from the United States. To bridge the gap a destroyer equipped with special generator facilities was dispatched to Kwajalein, to serve as the Kwajalein power supply station for as long as necessary. The amphibious members of the 2,750 Air Corps personnel stationed in the Marshalls brought ashore from a power boat the end of an electrical cable extending underwater to the destroyer.
For the 42,000 men of Joint Task Force One, daily rations and requirements included 70,000 candy bars, 40,000 pounds of meat, 89,000 pounds of vegetables, 4,000 pounds of coffee, 38,000 pounds of fruit, and 30,000 cigarettes. A recreation area at Bikini, constructed in March of 1946, included a beer garden, ice cream parlor, swimming beach, softball diamonds, courts for horse shoe pitching and volley ball, and table tennis. On the carrier Saidor the airplane elevator, raised to a level three feet above the main hanger deck, served as an improvised boxing ring for the servicemen. The Kenneth Whiting held inter-ship bouts on the seaplane deck. Many of the Task Force ships began to arrive at Bikini one by one. Most of these ships arrived via Pearl Harbor, which was humming with activity in preparation for Crossroads. Other Naval yards used for Crossroads preparations were Philadelphia, Terminal Island, San Francisco, Mare Island, Bremerton. The majority of the ships that sailed to Bikini would comprise the target “ghost” fleet, which would be exposed to the nuclear detonations. Since these ships were themselves scientific instruments of a grand scale it was necessary to place the ships, and their equipment and machinery, in good working order so the injury produced by the explosions could be accurately determined. Power plants, machinery, guns, turrets, and other equipment were placed in the best condition possible, and the watertightness of compartments tested and improved. Army trucks and tanks were hoisted aboard and made fast. Sturdy brackets and pedestals were installed to support the thousands of instruments to be mounted when the ships reached Bikini. For some installations special electric wiring was necessary. Among the ships that would make up the ghost fleet was the USS New York. Built in 1914, she was slow and overweight by 1946 standards. The New York saw action in both World War I and World War II, where she saw action off Iwo Jima and Okinawa. Attacked by Japanesse torpedoes, bombs, and artillery, she was hit only once, at Okinawa. The USS Nevada, painted bright orange for the tests, served as the target ship for the Able test. The battleship Pennsylvania, once a flagship of the U.S. fleet, as one of the five heavy ships in the target array. She served the United States for 29 years and was among the ships damaged at Pearl Harbor. The USS Saratoga, the third U.S. Aircraft carrier commissioned, was one of two carriers that made up the target array; the other carrier was the USS Independence.
The USS Arkansas was used also to be used in the target array and carried a variety of instruments for the nuclear explosions. The rugged supports on the starboard deck and on the top of the gun turret served as based for aluminum foil gages used to measure shock waves. Ground Forces equipment placed on various target ships, including the Arkansas, included heavy tanks, delicate radar and sound devices, flash proof clothing, fresh and canned rations, fuel and lubricants, numerous kinds of ammunition. Other ships used in the target array included the heavy cruisers USS Pensacola and USS Salt Lake City, and submarines Skate, Searaven, Skipjack, Tuna, Dentuda, Apogon, Pilotfish, and Parche. The German cruiser Prinz Eugen was one of the three foreign ships used in the target array. She was the second of the Admiral Hipper-class heavy cruisers built during World War II. She saw action in several important naval battles in the Atlantic, Baltic Sea, and English Channel, including the engagement in 1941 which resulted in the sinking of the Bismark. Following the war she was handed over intact to British Naval authorities. She made the voyage to America with a German crew, Americans replacing the Germans at Boston and Philadelphia. She was stripped of her armament at the Philadelphia Navy Yard prior to continuing to Bikini for Operation Crossroads. She was generally comparable in damage resistance to a U.S. Heavy cruiser. Other foreign ships included the Japanese battleship Nagato and light cruiser Sakawa. The Nagato was a 35,000 ton mainstay of Japan's navy and one of the two heaviest pre-war battleships. Commissioned in 1919, she was modernized in 1936. The Nagato was Admiral Isoroku Yamamoto's flagship, from which he heard the final code signal, "Tora! Tora! Tora!", informing him that the attack he engineered on Pearl Harbor was underway. In October 1944, when the Japanese attempted to choke off American landings in Leyte Gult, Nagato was part of the southern Japanese naval force which tried to force the San Bernardino Straits. In July 1945 she was heavily damaged by Navy carrier planes at the Yokosuka Naval Base. Following the war she was confiscated by U.S. Naval authorities. From 6 February through 11 May 1946, some 180 U.S. Personnel readied the Nagato for her voyage to Bikini for Operation Crossroads. She arrived at Bikini in late April following three weeks of repairs at Enewetak.
While Task Force ships arrived at Bikini, other preparations were being made for the shots. The instrumentation program was the heart of Operation Crossroads. More than 10,000 instruments were placed about on target ships, on shore and observer ships and aircraft. These included both simple and technically complex instruments. Many were familiar long before Crossroads while some were developed specifically for the nuclear tests. Various staff divisions under the Technical Director included: bomb operation, pressure and shack, wave motion and oceanography, electromagnetic propagation and electronics, radiological safety, radiation, radiometry, and technical photography.
The ships themselves were the main instruments of the operation. Their recorded behavior and response to nuclear detonations would reveal much of the nature and development of the forces created. Some of the instruments on the ships included those that measured roll and pitch, recorded strain experienced by plates and ribs, measured temperature of ship interiors, tested surrounding air for radioactive contamination. These measurements would be radioed to the observer fleet miles outside the lagoon. 3,030 rats, 176 goats, 57 guinea pigs, 109 mice, and 146 pigs were also used exposed to the experiments. They were placed on 22 target ships, in positions normally occupied by ship personnel. Some of these animals were dressed in clothing of various type and covered in anti-flash lotions and creams for biomedical thermal radiation studies. The National Cancer Institute supplied white mice with predilections for or against cancer. They were exposed in oder to determine whether the intense radiations would produce genetic changes. The mice were returned to the Institute immediately after Able shot to be bread and studies. For the Baker shot, only 200 white rats and 20 pigs were used on four target vessels. Animals used for the Able shot were not used in the Baker shot. Unmanned, radio-controlled boats and planes played an important part in the instrumentation aspect of the operation. The drone boats would enter the contaminated areas while it was still too ‘hot’ for human access and collect samples of water. Drone aircraft penetrated the mushroom cloud to collect radiochemical samples, performed photographic missions, and televised their instrument panel readings to remote onlookers. Operation Crossroads was a landmark in photography. Cameras, both still and motion picture, recorded the nuclear explosions and all its effects from every possible angle. Over 18 tons of photographic equipment was used for Crossroads. The Army Air Force camera roster totaled 328, including aerial motion and still cameras. More than 50,000 still and 1,500,000 feet of motion picture film were exposed during Crossroads. Enough film was exposed in a few seconds during Crossroads for 11 full length Hollywood productions. One camera, the world’s largest aerial camera at the time, used a 48-inch focal length telephoto lens capable of taking a legible photograph of the dial of a wrist watch a quarter mile away. Small gun sight cameras were also used to record the explosions. One high-speed camera operated at the rate of 10,000 frames per second.
The multiplicity of cameras was necessary to insure a wide variety of filter combinations, lenses, and exposures, and in general to ensure obtaining full records of results, particularly damage results. Two cameras were installed in gun turrets in F-13 aircraft. These cameras were controlled from the top fire control blister on the fuselage. These F-13 photographic aircraft used 16mm and 35mm type motion picture cameras capable of recording 2,000 frames per second. Rows of cameramen aimed their cameras down into the lagoon from C-54 aircraft. During shot Able the primary and secondary shockwaves were forceful enough to knock down one photographer caught off balance. These C-54 photographic planes had special apertures made in the fuselage to accommodate the cameras. Some of these planes carried as many as 28 cameras, still and motion picture. Photographic planes had to be exactly at their prescribed positions and altitudes, and on the prescribed course, at the time of the bomb drop, to permit accurate concentration of cameras on the designated parts of the target area. Accuracy of timing required great cooperation of air crews and photographers. This accuracy was achieved by through careful and detailed planning, and through rehearsals first held at Albuquerque, N.M, and later at the Marshalls. To supplement the roster of photographers an appeal was made to ex-servicemen with experience in photography to leave their civilian jobs temporarily and help during Operation Crossroads. Nearly one-half of the final photographic staff consisted of veterans brought back from civilian life. Ace photographers from Acme, International News Service, Associated Press, and Life Magazine were assigned to cover the tests. Photographs were handled under a pool agreement, all pictures in the pool being freely usable by pool members. The problem of security in releasing photographs was handled by a photographic panel representative of the varied responsibilities of the Task Force. At test Able were 166 newsmen, including 10 representatives of the foreign press. Two writers, one from the independent press and one from the wire services, were selected by the correspondents to write accounts of the tests as viewed from the air.
Cameras were also installed in the radio-controlled drone aircraft. B-17 drones had television cameras installed where the bomb sights would normally be located in the plexi-glass nose of the aircraft. These television cameras relayed what the drone plane saw to receivers miles away. The received images were studied by scientists and recorded on motion picture film. Television images of the drone’s instrument panel also helped the remote-control personnel keep the aircraft flying smoothly. The extreme humidity at Bikini presented a problem for the aerial photographers. As the photographic aircraft descended and the air pressure in the cabin increased, moisture would condense on the photographic film, destroying the emulsion. To avoid this problem, pilots descended very slowly, sometimes over a period as great as one hour. In many planes the difficulty was avoided by installing cameras in constant pressure chambers. At Kwajalein a huge photographic laboratory was built. This building was air cooled and dehumidified to prevent damage to the film. The majority of photographic work was done at the U.S. Naval Photographic Science Laboratory at Anacosita, D.C. Photographic training was conducted at San Diego by Navy carrier-based pilots. These pilots later made photo mosaics of Bikini Atoll and flew many photographic missions before and after each nuclear test, recording locations and conditions of target ships. In some of this work tri-metrogon cameras were used. These cameras are technically three separate cameras, with one lens pointed vertically downwards and the other two pointed to the left and right to cover all the remaining field from horizon to horizon. For this photographic work, the Navy used six Navy F6F-5Ps, four TBMs, three PBMs, and four F6F drones. Cameras in these planes were in some instances accurately synchronized with cameras on towers and on surface ships in order to show the test from various angles at the same instant.
Instruments were installed on top of steel towers erected on various islands surrounding the Bikini lagoon. Television cameras on these towers were focused on the target array and transmitted their signals in real time to receivers miles away during the moment of the explosions. Still and motion picture cameras were also installed in these towers to make permanent photographic records. Towers were assembled on the ground and hoisted into place. Cameras were installed inside lead-walled vaults, the doors of which were arranged to close automatically after filming had been accomplished, to protect the film from the damaging effects of gamma radiation. Cameras were started remotely prior to the shots. Pyramidal orientometers were set up on target ships. These devices indicated the direction from which the heat and radiation from the atomic bomb came, in terms of burns produced when radiation passed through the small holes on the base of the instruments. Sonobouys were set up to measure underwater sound waves produced by the atomic explosions. Each sonobouy consisted of delicate listening apparatus beneath the floats which housed an automatic radio transmitter.
Dr. Marshall Hollowway headed the Los Alamos Laboratory group at Bikini. He was charged with the heavy responsibility of preparing the two atomic bombs used in the Crossroads tests. Dr. Ernest Titterton, a British scientist and one of Dr. Hollowway's principle assistants, was appointed to advise the Naval Research Laboratories in Washington, D.C. on the timing requirements. Despite the passing of the McMahon Act, which prohibited all but U.S. nationals from working on nuclear weapons, Titterton and another British scientist, William Penney, were asked to serve on Operation Crossroads due to their expertise in timing measurements and shock-wave studies, respectively. Titterton became very popular with the crew of the ship he sailed on to Bikini as he gave them simple lectures on the bomb tests. He also repaired the ship's movie projector. In preparation for the Crossroads nuclear tests, a number of scaled model experiments were conducted at the Taylor Model Basin near Washington, D.C. To aid in estimating the size and character of waves that would be produced by the actual atomic detonations. Scale model ships were constructed of thin sheets of brass and floated in the test pool. Scaled amounts of TNT were used to simulate the atomic explosions. These tests were made in a specially constructed tank known as “Little Bikini”. Other studies were made on a larger scale, using 500-pound amounts of explosive, in tests conducted at the Naval Mine Warfare Test Station at Patuxent, Maryland. In both types of scaled experiments effects noted were the size of the water crater, height, persistency and diffusion of plumes. Tail markings of B-29 aircraft served to identify their specific functions as part of Task Force Group 1.5. “F” markings indicate B-29s modified for use as photographic ships. An arrow in a circle marked a plane used to drop air-pressure gages from high altitude during the first test. A “B” stood for a B-29 bomber. “W” identified weather planes. A special floating laboratory was set up on the Bowditch for the oceanography section of the Task Force. Over 20,000 fish were caught by hook, bet, and seine. Sonar acoustical devices were used to locate schools of fish. Some fish were caught by swimmers armed with spears and wearing face masks. Some fish samples were brought back to Washington D.C. For study. However, a large number of the specimens gathered were lost when the YP 636 carrying them went aground south of San Fransisco. Ten representatives and four Senators journeyed to Bikini to the view the tests. Two of the Senators, Carl A. Hatch (D) of New Mexico and Leverett Saltonstall (R) of Massachusetts, were members of the President's Evaluation Commission set up by President Truman to supplement the Evaluation board created by the Joint Chiefs of Staff. Eleven foreign nations had members that made up the United Nations Foreign Observer Group. These countries included Australia, Brazil, Canada, China, France, Egypt, Great Britain, Mexico, Netherlands, Poland, and the U.S.S.R.
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Baker, the second shot of Operation Crossroads, was the world's fifth nuclear explosion, third nuclear test, and first underwater nuclear explosion. As soon as the extent of damage from Able had been determined, CJTF 1 tentatively set 25 July for Baker. The news media ship USS Appalachian returned to Pearl Harbor to allow some media people to depart and others to join the group. Some observers were taken a cruise to Ponape, Truk, Majuro, and Guam islands while the Task Force prepared for Baker.
Several target ships had sustained boiler and/or stack damage. Wreckage was cleared and repairs made so that every target ship was able to steam under its own power on at least one boiler. USS Independence needed considerable work to ensure watertight integrity. The submarine Skate needed superstructure repairs, including a temporary bridge. One by one the target ships were moved to their positions in the new target array for Baker. Able blast damage inspections were completed and new instrumentation and new experiments were set up on these target ships in preparation for Baker. Some turnover of Task Force personnel occurred following Able. A continuous training program was in effect after Able to train new personnel in preparation for Baker. A large quantity of radiac instruments was received during this period, alleviating a minor shortage experienced during Able. The underwater Baker was expected to create a much larger radsafe problem and require more radiac meters than did Able. Army Air Forces conducted a major rehearsal on 14 July. All Army air units participated. Locations, communications, and coordination were tested, checked, and rechecked. Then on 19 July, JTF 1 conducted a full-scale dress rehearsal, dubbed "William Day." All units of the Task Force participated fully except the air task units. Heavy cloud cover and rain limited aircraft participation in the rehearsal. On D-1 (24 July) CJTF 1 confirmed Baker Day as 25 July and designated shot time for 0835. Weather forecasts indicated that there would be favorable weather on that day. Evacuation of Task Force ships and personnel began immediately. Personnel and ships not needed immediately after the shot were evacuated to Rongelap Atoll instead of Kwajalein because it was closer to Bikini. Saint Croix evacuated 607 U.S. personnel and natives from Enewetak on 21 July.
The day before Baker, two C-54s were again sent to Enewetak and Roi islands to transport the cloud samples to Kwajalein on 25 July. Five C-54s were again positioned at Enewetak in case evacuation of essential personnel was necessary. Except for minor changes, the aircraft missions were similar to the Able shot missions. By 1735 on 24 July all but 13 support ships were clear of the lagoon. These cleared the lagoon by 0700 the following morning. Task force personnel on the islands at Bikini were evacuated by 1555 on 24 July. Three sailors on USS Gasconade, a target ship, were somehow overlooked. They filled the yardarms with bunting (the signal that they needed evacuation) and were picked up by USS Conserver at 0530 on 25 July The bomb was suspended 90 feet beneath the surface of the lagoon from medium landing ship LSM-60. The LSM had been extensively modified to provide rigging facilities, a laboratory, and special radio receivers and transmitters. The bomb was encased in a strong, watertight, steel caisson and had a coaxial cable running from it to the LSM. The TG 1.1 laboratory personnel associated with the bomb arming were evacuated from LSM-60 at 0545 on 25 July. There were 68 target vessels in the array for Test Baker. Twenty-four small craft were beached on Bikini Island. The submarine USS Searaven (which had been submerged on 24 July), partially surfaced later in the day. It was finally resubmerged by 2300 on 24 July. Of the eight target submarines, six were submerged and two were on the surface for the test. Weather was not quite as important for Baker as for Able because the underwater detonation was expected to limit the cloud height and thus localize the radioactivity. Good visibility, however, was important for photography. Baker was detonated on schedule at 0835 on 25 July 1946. The detonation command was sent by radio using coded signals.
Another aircraft observer reported seeing a major ship "on [its] nose" before it sank and saw a water wave pass over one of the small islands between Bikini and Eneu islands about 2 minutes after the detonation. When the air over the fleet cleared, Arkansas, LSM-60, and four LCTs were not in sight. Saratoga was listing to starboard and her stern was low. The underwater explosion inflicted heavy damage on the target fleet. Eight ships were sunk or capsized. Eight ships were immobilized or seriously damaged. Generally, ships beyond 1,500 yards were undamaged. Those between 1,100 and 1,500 yards sustained only slight damage. Those between 900 and 1,100 yards suffered moderate damage. Those inside 900 yards were seriously damaged or were sunk.
At 0912 the drone control ship, Beqor, began moving two drone boats from the lee of Eneu towards the target array using directions from the orbiting drone control TBMs as in Able. Each boat took ten 5-gallon samples of lagoon water and by 1030 was en route back to its anchorage. The drone boats were so radiologically contaminated that boarding parties from Beqor could not go aboard. The drone boats were taken to USS Albemarle where the water samples were finally removed about 1430. Two additional drone boats were guided into the target area the same afternoon using the same combination of TBMs and Beqor. Each took 10 samples of water, which were transferred to Albemale about 1800. Albemarle then headed for Kwajalein with the samples. Four more runs were made on 26 July and two more on 27 July using the same control procedures. The radiation intensities had lessened somewhat, allowing boarding parties from Beqor to remove these samples and transfer them to USS Haven.
Early reports from radiological reconnaissance PBMs and drone boats indicated that the lagoon and surrounding atmosphere were intensely radioactive. One drone boat recorded about 730 R/24 hours near the center of the target array. The three PBMs made several passes over the lagoon on 25 July, starting at 4,000 feet, then at 3,000, 2,000, 1,000 and 500 feet; the first pass was made at 0915 and the last at 1615. Reentry into the lagoon commenced at 0916 when the PGM and LCPL radiological patrol boats with monitors aboard entered. They were closely followed by TU 1.2.8 and Kenneth Whitinq. Fall River took up its position at the lagoon entrance at 0947 to control entry and exit. The Salvage Unit entered the lagoon at 1015 and began checking and boarding target vessels. A total of 49 support ships with 14,920 personnel entered the lagoon by the end of 25 July. For Baker, ten initial boarding teams were established , a total of 86 men, including one monitor for each team. These teams were the first groups to return to the target vessels, although five of the firefighting officers may not have actually reboarded unless there was a fire to fight In addition, representatives of the groups responsible for the scientific experiments and tests of military equipment returned to retrieve data and materials when given permission by the monitors. Film and other data were recovered from Bikini and Eneu islands during the afternoon. Twelve target ships were temporarily boarded, ten of which were declared radiologically safe (no radiation measured above 0R./12 4 hours) before nightfall on 25 July. The remaining target ships were too radioactive to board and the water near the detonation site remained radioactive as well.
The radioactive cloud had apparently moved north of the burst. Radiological reconnaissance F-13s discovered weak radioactivity while flying 43 nmi north of the lagoon at 1318 and a highly radioactive cloud at 80 mi almost directly north of Eneu Channel at 1610. An F-13 due west of Bikini at 50 nmi made no contact with radioactivity by 1415. Apparently based on this information, the alert at Enewetak Atoll west of Bikini was dropped at 1418 and clearance was given to return evacuees there. At about 1608 Saratoga sank. Radiological conditions prevented any attempt to save the ship.
The radioactivity persisted through 26 July. Films from cameras on Aomen Island were recovered using helicopters. An oil slick with radioactive debris was observed north of Nam Island outside the lagoon. Task Force ships in the lagoon stayed in the southeast sector near the entrance in order to keep clear of the radioactive water. Their evaporators were allowed to be used on 26 July. The USS Hughes was towed to Eneu and beached by the USS Reclaimer to prevent sinking. The same situation persisted on 27 July however, some instrumentation was recovered from the target ships. USS Preserver attempted to get a line aboard the damaged and heavily contaminated USS Fallon so that it could also be beached beside the Hughes. This could not be accomplished until the following day. Because of the persistent radiation in the lagoon, several radiological reconnaissance flights took place over the next few days. Eight missions were flown on 26 July and two on 27 July. Five photography flights were made on 26 July and four on 27 July. Six drone boat control TBMs flew on 26 July and two on 27 July. Photo and radiological reconnaissance flights continued through 30 July, while drone boat control flights were not needed after 28 July. On 28 July, radioactive water in the lagoon spread southeast to some of the Task Force ship anchorage areas, forcing some ships to relocate to uncontaminated areas. On 28 July at 2352, Summer reported readings of 0.156 R/24 hours on outboard bunks and 0.204 R/24 hours at the evaporators. On 29 July it was sent out of the lagoon and into the open sea in an attempt to decontaminate the hull. PGM-24 and PGM-29 had become contaminated earlier, reading 1.56 R/24 hours amidships. Their crews were evacuated to USS Appling and Haven. Some test animals were recovered from target ships. By 29 July it was apparent that the target fleet was much more heavily contaminated then had been expected. This contamination resulted in the cancelation of the third deep underwater test code named Charlie. The inspection and documentation of Baker's effects could not proceed if target vessels were too contaminated for reboarding and thorough examination.
During the fourth night after Baker the Nagato sank. The next day, resurfacing of submarines continued, as did the recovery of animals from the target ships. The radiological situation improved slightly, allowing a few more target ships to be boarded. Pieces of highly radioactive steel, probably from LSM-60, were found on the deck of the USS Pensacola. On 30 July most target ships remained too radioactive for boarding; however, radioactivity of the lagoon water continued to decrease. The last of the animals were removed from the target array. Although most animals were located below deck, the great majority of them died by 1 November 1946. In nearly all case, the cause of death was gamma radiation resulting from Baker's radioactive rain out and base surge. Also, many of the fish in the northeast corner of the lagoon were killed by the explosion. On 31 July, Bikini Island was declared safe and personnel were permitted to go ashore. The beaches were declared off limits due to the radioactive debris which had washed up on shore. Many target vessels remained too radioactive to board and the persistent radioactivity on these ships made the prospect of reboarding “very discouraging”. The lagoon water, except near the bottom, had reached safe levels by the evening of 31 July. Complete recovery of instrumentation and records was not completed until 7 August. On 8 August, CJTF 1 requested authority from the Chief of Naval Operations to decommission, or place out of service, 38 target vessels at Bikini. argued that the ships were in such radiological condition that with available personnel and equipment they could not all be made safe for the work needed either to prepare them for movement to Pearl Harbor or to assess their damage fully. By 11 August it was recognized that post-Baker contamination was also a continuing and increasing problem for nontarget ships remaining in Bikini Lagoon. Radioactive material from the contaminated lagoon was accumulating in the support ships' evaporators, saltwater piping, and marine growth on the outside of their hulls. Plans were made to move target vessels and support ships to Kwajalein, a convenient location with good anchorages, where the problems resulting from Baker could be faced free from the environmental contamination present at Bikini. Beginning 19 August, 53 target ships were towed to Kwajalein and by 5 September the last of the target fleet had left Bikini. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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