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    Operation Crossroads - 1946

    / Main Archive / USA /



    Page: 1/3


    "The bomb will not start a chain-reaction in the water converting it all to gas and letting the ships on all the oceans drop down to the bottom. It will not blow out the bottom of the sea and let all the water run down the hole. It will not destroy gravity. I am not an atomic playboy, as one of my critics labeled me, exploding these bombs to satisfy my personal whim."

    - Vice Admiral W.H.P. Blandy, Commander of Joint Task Force One


    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measures could be taken by a ship attacked with atomic weapons, and whether traditional tactical practices were outdated.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 on 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. 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.

    Target Fleet

    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 yards 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.


    "The atom bomb is here. It exists. We must look to the future. Up until now only three have been exploded, and none over the water. It is the duty of the military services to explore the military might of this new weapon. We want to be prepared for any use of atomic energy that may become necessary, whether offensive or defensive."

    - Major General W.E. Kepner, Deputy Task Force Commander for Aviation

    Bikini Atoll


    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 3.200 km southwest of Hawaii and 6,700 km from San Fransisco. 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 60 meters and provided good anchorage for the target fleet. Bikini is located some 400 km 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.

    US plans being explained to King Juda

    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 concrete cisterns for catching rainwater were built. A total of 87,000 liters 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 inedible. 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 healthy 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.

    For the 42,000 men of Joint Task Force One, daily rations and requirements included 70,000 candy bars, 18,000 kg of meat, 40,000 kg of vegetables, 1,800 kg of coffee, 17,000 kg 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 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.

    USS Nevada

    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, was 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, was one of two carriers that made up the target array; the other carrier was the USS Independence.

    - Video of the USS Nevada and the target fleet

    The USS Arkansas was also to be used in the target array and carried a variety of instruments for measuring the nuclear explosions. The rugged supports on the starboard deck and on the top of the gun turret served as a base 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 and 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.

    Other foreign ships included the Japanese battleship Nagato and light cruiser Sakawa. 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. 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.

    The ships themselves were the main instruments of the operation. Their recorded behavior and response to nuclear detonations would reveal much of the nature 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 interior and, tested surrounding air for radioactive contamination. These measurements would be transmitted by radio to the observer fleet miles outside the lagoon.

    Goats penned on the USS Nevada
    3,030 rats, 176 goats, 57 guinea pigs, 109 mice, and 146 pigs were to be exposed during 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 order 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 500,000 meters 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 122 cm focal length telephoto lens capable of taking a legible photograph of the dial of a wrist watch half a kilometer 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. The building was 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.


    Photography of Operation Crossroads

    More than 50,000 still and 500,000 meters of motion picture film were exposed during Crossroads. Since the fourth and fifth nuclear explosions ever fired were during Crossroads, every effort was made to make extensive visual records.

    - Click on thumbnails for a larger version






    Instrumentation was 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. 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.

    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 more explosives, 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 indicated B-29s modified for use as photographic platforms. 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.

    Ten representatives and four Senators journeyed to Bikini to the view the tests. Two of the Senators, Carl A. Hatch of New Mexico and Leverett Saltonstall 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.



    Dave's Dream


    Winners of a hotly contested competition in which the country's finest very-heavy-bomber crews took part, the crew of the B-29 bomber Dave's Dream won the mission to drop the Able bomb during Operation Crossroads. This aircraft was originally called Big Stink.

    It participated in the atomic bombing on Nagasaki on August 9, 1945. Assigned to the 393rd Bomb Squadron, 509th Composite Group, it was used as a camera plane in support of the bomb-carrying aircraft called Bockscar, to photograph the explosion and effects of the bomb, and also to carry scientific observers.

    Built at the Glenn L. Martin Aircraft Plant at Omaha, Nebraska, the aircraft was accepted by the Army Air Forces on April 20, 1945, and flown to Wendover Army Air Field, Utah in May. It departed Wendover for Tinian on June 19 and arrived on June 24. There it was assigned victor number 10, but that was changed for security reasons to victor 90 on August 1. On July 23, 1945, with Col. Paul Tibbets at the controls, it dropped a dummy Little Boy bomb assembly off Tinian to test its radar altimeter detonators.

    After the war it served with the 509th CG at Roswell Army Air Field. In April 1946, after being assigned to Operation Crossroads, it was renamed Dave's Dream by its crew in honor of Captain David Semple, a bombardier who had been killed in the crash of another B-29 on March 7, 1946, near Albuquerque, New Mexico. Semple had been a bombardier in many of the 155 test drops for the Manhattan Project.



    The Tests




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