W47

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 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.

Live fire testing

The W47 is the only US ICBM or SLBM warhead to have been live fired 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. Whilst 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. [See Donald A. MacKenzie, "Inventing accuracy: a historical sociology of nuclear missile guidance" (Cambridge, Mass.: MIT Press, 1990).]

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.

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. [See for example [http://www.fas.org/sgp/crs/nuke/RL32929.pdf "Nuclear Weapons: The Reliable Replacement Warhead program"] , Jonathan Medalia, 2005, Congressional Research Service.]

ee also

* UGM-27 Polaris
* List of nuclear weapons

References

External links

* [http://nuclearweaponarchive.org/Usa/Weapons/Allbombs.html Allbombs.html list of all US nuclear weapons at nuclearweaponarchive.org]
* [http://nuclearweaponarchive.org/Usa/Tests/Dominic.html Dominic nuclear test series, including Frigate Bird Polaris/W47 flight test]