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    Operation Ranger - 1951

    / Main Archive / USA /

    Fox 06/02/1951
    The intensifying Cold War, which spread into direct nuclear competition in 1949 with the first Soviet atomic test, spurred the U.S. to expand its efforts to improve it's nuclear arsenal. Operation Ranger was the first nuclear testing series conducted at the Nevada Test Site, then called the Nevada Proving Grounds. Sponsored by the Atomic Energy Commission (AEC), Ranger was conducted between January 25 to February 6, 1951.

    The series featured five nuclear detonations and a single, high explosives test fired on January 25, 1951 to calibrate equipment for the upcoming nuclear tests. The series was intended to provide data for use in determining design criteria for nuclear devices scheduled for detonation at Operation Greenhouse, to be conducted at the Pacific Proving Grounds from April 7 to May 24, 1951. Ranger saved the weapons development program months of time and helped test the concept of small, atomic weapons.

    In November 1950, the Los Alamos Scientific Laboratory discovered that insufficient data were available to determine satisfactory design criteria for nuclear devices to be tested in Operation Greenhouse. The LASL scientists believed that variations in the compression of the critical material could affect the yields of the Greenhouse devices.

    To confirm this hypothesis, LASL held conferences on December 6 and 11, 1950 and concluded that a series of small nuclear tests should be conducted to improve the Greenhouse design criteria. On December 22, 1950, LASL requested approval for a continental series from the AEC Division of Military Application (DMA). DMA approved the request and asked for Presidential approval to expend the fissionable material required for the series. The White House responded affirmatively on January 11, 1951, formally creating Operation Ranger.

    The same day that Operation Ranger was approved by the President, the AEC distributed its only announcements of the series. Handbills were circulated in the area of the NTS stating that from January 11, 1951 nuclear tests would be conducted at Las Vegas Bombing and Gunnery Range.

    Operation Ranger was the first time nuclear devices were detonated within the continental United States since the Trinity test in 1945. The series was hastily arranged and a relatively small series compared to subsequent operations at the NTS. 360 Department of Defense personnel participated in air support services, scientific experiments, weather support, communications security and observer programs. Since Ranger was only a 13-day operation, the same units and participants performed the same duties throughout the series.

    The Nevada Test Site was divided into two geographical areas: Yucca Flat and Frenchman Flat. Yucca Flat, located in the north-central part of the NTS, is a 497 square kilometer desert valley surrounded by mountains. This area was the location of many nuclear detonations after Operation Ranger. Frenchman Flat, which includes a 23 square kilometer dry lake, is located in the southeastern part of the NTS.

    The Ranger Control Point, which served as AEC operational headquarters, was 13 kilometers south of ground zero. It was a hastily constructed building that included a control room, administrative office, first-aid station, and shower for personnel decontamination. Two photography stations were located near ground zero. One station was 3.2 km to the southeast on the dry lake. The lake bed also served as the Frenchman Flat landing strip because of its smooth, hard surface. The other station was 3.2 km northeast of ground zero.

    The Scientific Tests Section of the Test Group administered projects at each nuclear detonation. DoD personnel were involved in eight projects at each test except for the Baker shot, where they took part in seven experiments. Film badges, fabrics, and other materials and instruments were placed in or around military fortifications constructed in the ground zero area. Equipment was retrieved after the detonation, when radiation levels had decreased and limited access into the shot area was permitted.

    Mk-6 Bomb

    Three samples of U-238 metal, each approximately onekilogram (2.2 lbs.), were put on posts near surface zero to measure the fissions induced from both gamma rays and neutrons emanating from the airbursts. This experiment was intended to answer a militarily-significant question: How closely together in time and space could two atomic bombs be detonated without the gamma rays and neutrons from the first detonation causing serious predetonation of the second?

    A "Pajarito" assembly for testing criticality was used, involving a mockup of a bomb with a sphere of plastic material simulating HE. The name "Pajarito" was a reference to the site near Los Alamos where critical and subcritical assemblies were tested remotely following the accidental deaths of two physicists in August 1945 and May 1946; some assemblies simulated stockpiled weapons. The "Pajarito" assembly for Ranger contained all nuclear components, with counters in the pit to record the rate of induced nuclear reactions versus time. While this experiment was primarily an earlytest of "fratricide," the effects of nuclear warheads exploding near each other, the effects of various radiations on relatively-large pieces U-238 was also useful in the design of the Sausage thermonuclear device to be tested in the fall of 1952.

    All five nuclear devices were dropped from B-50 bombers over Frenchman Flat from a height of 330 m above the ground with the exception of the Fox shot, which was airdropped from a height of 440 m. The first four devices were modified Mk-4 weapons, designed to test different design parameters for yield. The last shot, Fox, was a test of the new Mk-6 weapon and proof tested the Fox composite core. All of the nuclear devices weighed 4,900kg and had 152 cm diameters. The high explosive assembly, core, and firing system of each device weighed 3.220 kg.

    Primary Army participation came from the 82nd Reconnaissance Battalion from Fort Hood, Texas, which provided security at the test site. The number of observers at Ranger has been documented as 156, but only three of these are believed to have been military personnel.

    Observers were invited to view the detonations to demonstrate the AEC's ability to conduct safe nuclear testing within the continental United States. The AEC invited influential political figures, especially members of Congress, to accompany AEC and high-ranking military officials in witnessing the Ranger detonations. On shot-day, the observers were given an orientation lecture at the AEC Las Vegas office before being driven by bus to the NPG. There they were escorted by Security Group personnel to an observation area, where they witnessed the detonation. The observation area was located approximately 400 meters south of the AEC Control Point.

    Test Shots

    Video Name Yield Date |UTC| Type Warhead Location LAT/LONG
    - Able 1 Kt 13:44 27/01/1951 Airdrop @320m Mk-4 Frenchman Flat-Nevada 36.80000 -115.95000
    - Baker-1 8 Kt 13:52 28/01/1951 Airdrop @330m Mk-4 Frenchman Flat-Nevada 36.80000 -115.95000
    - Easy 1 Kt 13:46 01/02/1951 Airdrop @330m Mk-4 Frenchman Flat-Nevada 36.80000 -115.95000
    - Baker-2 8 Kt 13:48 02/02/1951 Airdrop @340m Mk-4 Frenchman Flat-Nevada 36.80000 -115.95000
    - Fox 22 Kt 13:47 06/02/1951 Airdrop @440m Mk-6 Frenchman Flat-Nevada 36.80000 -115.95000

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    Published on: 2010-09-12 (2632 reads)

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