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 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 . 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 . While stationed off Johnston Island , the American submarine USS Ethan Allen fired a Polaris - A2 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 . Reliability controversy . The history of the W47 warhead had a serious series of reliability problems 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 problems 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 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 safe 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 .