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M101 20mm Davy Crockett Spotting Round

A historical DU round, used by the US to estimate firing trajectory on the Davy Crockett nuclear rifle. No longer in use.

  • Produced between 1956 and 1963
  • Used in practice on US bases until the late 1960s, or early 1970s
  • Contamination of bases uncovered in 2006

Old M101 round. The main body of the round has corroded significantly.















The M101 was fired from a small 20mm rifle attached to a larger barrel, as part of the Davy Crockett weapons system. The Davy Crockett was a battlefield nuclear weapons system, fired from the ground by either the M28 or M29 freestanding tripod lancher. The M101 was not the main round for this weapon, but a spotting round.

The purpose of the Davy Crockett was to prevent the advance of oncoming enemy troops, by the power of the explosion, and the deterrent effect of irradiating an area. The Davy Crockett projectile, the M388, could carry either conventional explosives, or the W54 nuclear warhead.

The W54 had an explosive yield of 0.01 kilotonnes, according to most sources, although some state that the operator could select a yield of between 0.01 and 0.25 kilotonnes. Either way, the short range of the weapon meant that those firing it would have also received a substantial radiation dose.

The Davy Crockett was produced between 1954 and 1963, but remained in service until 1971. It was never fired in anger, but was fired in two tests on the Nevada Test Range in 1962. The second test was part of 'Operation Ivy Flatts', which involved a nuclear exercise as part of a battle simulation involving live troops. This was the last atmospheric nuclear test carried out by the US.

M28 Davy Crockett nuclear recoilless rifle

Of the two launchers, only the M28 fired the 20mm M101 DU Spotting round. The M29 launcher had a longer range, and the spotting round was a 37mm non-DU round. On the M28, the M101 was fired from a smaller barrel, below the main one (visible right), and would follow a similar trajectory to the warhead. Therefore, it was used to estimate the targetting and range of the gun. The M101 weighed around 450g, and measured about 20cm long. Each round is estimated to contain around 192g of uranium.

During its service life, the existance of the Davy Crockett was a closely held military secret, and little was known about its deployment, or the use of the M101 in practice. Despite the longstanding claims of campaigners, the US military denied that it had used DU on its bases in Hawaii. However, in 2005, information came to light which drew attention to the past use of the M101 on the Schofield Barracks on Oahu Island, between 1962 and 1968.

Military fieldwork confirmed the presence of spent M101 rounds, and of uranium contamination, and the army was obliged to apply for a site license under the US Nuclear Regulatory Commission (NRC) for the Schofield Barracks and Pohakuloa Training Area. All sites connected with radioactive materials require such licenses under US law, including sites with historic contamination of the ground.

Other sites where M101 fragments have been found include: Fort Hood, Texas; Fort Benning, Georgia; Fort Campbell and Fort Knox, Kentucky; Fort Carson, Colorado; Fort Lewis, Washington; and Fort Riley, Kansas. Use of the M101 is also suspected in the Aberdeen Proving Ground, Maryland; Fort Dix, New Jersey; and Makua Military Reservation, Hawaii.

In total 75,318 M101 rounds were produced, according to the NRC. Of these, around 44,000 are known to have been decommissioned in the 1970s, and around 2,000 are known to have been fired at the Lake City Army Ammunition Plant in the 1960s. As such, approximately 29,318 M101 rounds are not accounted for, and are likely to have been fired in the bases where the Davey Crockett was based. Aside from the sites listed above, upon production the M101 was also shipped to the following locations: Frankfurt , Germany; Inchon, South Korea; Pirmasens, Germany; Ryukus Island, Okinawa, Japan. It is not known whether these locations were the final destinations of the rounds, or whether they were then moved elsewhere.