W47
Encyclopedia
The W47 was an American thermonuclear warhead used on the Polaris A-1
sub-launched ballistic missile system. Various models were in service from 1960 through the end of 1974. The warhead was developed by the Lawrence Radiation Laboratory
between 1957 and 1960.
The W47 was 18 inches in diameter and 47 inches long, and weighed 720 pounds in the Y1 model and 733 pounds in the Y2 model. The Y1 model had design yield of 600 kilotons and the Y2 model had a doubled design yield of 1.2 megatons
.
The W47 was the first warhead with a new, miniaturized pit
. The aerodynamic flare at the base provided stability of orientation during descent. Two small rocket motors were used to spin the warhead for better stability and symmetry during reentry.
in an atmospheric missile and warhead test, on May 6, 1962. This event took place during shot Frigate Bird which was part of the Dominic test series. While stationed off Johnston Island, the American submarine USS Ethan Allen
fired a Polaris-A1 missile at an open ocean target point in the vicinity of Palmyra Atoll
, south of Hawaii
. The missile travelled a distance of 1,020 miles. The test was observed by two submerged US submarines stationed approximately 30 miles from the target point, the USS Carbonero
and the USS Medrigal
. The missile warhead detonated at 23:30 GMT on May 6, 1962, approximately 2 km from the designated target point, and at the target altitude of 11,000 feet. The detonation was successful and had the full design yield of approximately 600 kilotons. The shot was designed to improve confidence in the US ballistic missile systems, though even after the test there was considerable controversy. This was partly because it was revealed that the warhead selected for the test had undergone modifications before testing and was not necessarily representative of the stockpile.
A number of the Polaris warheads were replaced in the early 1960s, when corrosion
of the pits was discovered during routine maintenance.
Failures of the W45
, W47, and W52
warheads are still an active part of the debate about the reliability of the US nuclear weapons force moving into the future, without ongoing nuclear testing.
A one-point safety test performed on the W47 warhead just prior the 1958 moratorium failed, yielding a 100-ton explosion. As the test ban disallowed testing needed for inherently one-point safe design, a makeshift approach with a boron
-cadmium
wire folded in the pit during manufacture, and pulled out by a small motor during the warhead arming. The wire had a tendency to become brittle during storage, and break or get stuck during arming, preventing complete removal and rendering the warhead a dud. It was estimated that 50-75% of warheads would fail. This required a complete rebuild of the W47 primaries. The oil used for lubricating the wire also promoted corrosion of the pit.
UGM-27 Polaris
The Polaris missile was a two-stage solid-fuel nuclear-armed submarine-launched ballistic missile built during the Cold War by Lockheed Corporation of California for the United States Navy....
sub-launched ballistic missile system. Various models were in service from 1960 through the end of 1974. The warhead was developed by the Lawrence Radiation Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
between 1957 and 1960.
The W47 was 18 inches in diameter and 47 inches long, and weighed 720 pounds in the Y1 model and 733 pounds in the Y2 model. The Y1 model had design yield of 600 kilotons and the Y2 model had a doubled design yield of 1.2 megatons
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...
.
The W47 was the first warhead with a new, miniaturized pit
Pit (nuclear weapon)
The pit is the core of an implosion weapon – the fissile material and any neutron reflector or tamper bonded to it. Some weapons tested during the 1950s used pits made with U-235 alone, or in composite with plutonium, but all-plutonium pits are the smallest in diameter and have been the standard...
. The aerodynamic flare at the base provided stability of orientation during descent. Two small rocket motors were used to spin the warhead for better stability and symmetry during reentry.
Live fire testing
The W47 is the only US ICBM or SLBM warhead to have been live firedLive fire exercise
A live fire exercise or LFX is any exercise in which a realistic scenario for the use of specific equipment is simulated. In the popular lexicon this is applied primarily to tests of weapons or weapon systems that are associated with the various branches of a nation's armed forces, although the...
in an atmospheric missile and warhead test, on May 6, 1962. This event took place during shot Frigate Bird which was part of the Dominic test series. While stationed off Johnston Island, the American submarine USS Ethan Allen
USS Ethan Allen (SSBN-608)
USS Ethan Allen , lead ship of her class, was the second ship of the United States Navy to be named for American Revolutionary War hero Ethan Allen....
fired a Polaris-A1 missile at an open ocean target point in the vicinity of Palmyra Atoll
Palmyra Atoll
Palmyra Atoll is an essentially unoccupied equatorial Northern Pacific atoll administered as an unorganized incorporated territory by the United States federal government...
, south of Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. The missile travelled a distance of 1,020 miles. The test was observed by two submerged US submarines stationed approximately 30 miles from the target point, the USS Carbonero
USS Carbonero (SS-337)
USS Carbonero was a Balao-class submarine, the first ship of the United States Navy to be named for the carbonero, a salt-water fish found in the West Indies. Her keel was laid down on 16 December 1943 by the Electric Boat Company of Groton, Connecticut. She was launched on 19 October 1944...
and the USS Medrigal
USS Medregal (SS-480)
USS Medregal , a Tench-class submarine, was the only ship of the United States Navy to be named for the medregal, a streamlined, fast-swimming, bluish-colored fish of the jack family which abounds in waters of the West Indies and in the Atlantic as far north as the Carolinas.Medregals keel was laid...
. The missile warhead detonated at 23:30 GMT on May 6, 1962, approximately 2 km from the designated target point, and at the target altitude of 11,000 feet. The detonation was successful and had the full design yield of approximately 600 kilotons. The shot was designed to improve confidence in the US ballistic missile systems, though even after the test there was considerable controversy. This was partly because it was revealed that the warhead selected for the test had undergone modifications before testing and was not necessarily representative of the stockpile.
Reliability controversy
The history of the W47 warhead had a serious series of reliability issues with the warhead design. 300 of the EC-47 production prototype model were produced from April 1960 through June 1960, and were all promptly retired in June 1960 due to reliability concerns. Production of Y1 and Y2 models then proceeded in 1960 through 1964. A total of 1060 Y1 and Y2 models were produced, but they were found to have so many reliability issues that no more than 300 were ever in service at any given time. In 1966, 75% of the stockpiled Y2 warheads were thought to be defective and unusable. Repair programs continued for some time.A number of the Polaris warheads were replaced in the early 1960s, when corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
of the pits was discovered during routine maintenance.
Failures of the W45
W45
The W45 was a multipurpose American nuclear warhead developed in the early 1960s, first built in 1962 and fielded in some applications until 1988. It had a diameter of 11.5 inches , a length of 27 inches and weighed 150 pounds . The yields of different W45 versions were 0.5, 1, 5, 8, 10, and 15...
, W47, and W52
W52
The W52 was a thermonuclear warhead developed for the MGM-29 Sergeant short-range ballistic missile used by the United States Army from 1962 to 1977. The W52 is 24 inches in diameter and 57 inches long, and weighed 950 pounds. It had a yield of 200 kilotons...
warheads are still an active part of the debate about the reliability of the US nuclear weapons force moving into the future, without ongoing nuclear testing.
A one-point safety test performed on the W47 warhead just prior the 1958 moratorium failed, yielding a 100-ton explosion. As the test ban disallowed testing needed for inherently one-point safe design, a makeshift approach with a boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
-cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
wire folded in the pit during manufacture, and pulled out by a small motor during the warhead arming. The wire had a tendency to become brittle during storage, and break or get stuck during arming, preventing complete removal and rendering the warhead a dud. It was estimated that 50-75% of warheads would fail. This required a complete rebuild of the W47 primaries. The oil used for lubricating the wire also promoted corrosion of the pit.