Earlier this year Sandia National Laboratories fired a nuclear warhead out of a cannon in New Mexico. The reason you didn't hear an earth-shattering kaboom is because it was an inactive weapon that was fired into a tank of water as part of a federal program to improve the longevity and effectiveness of the US nuclear stockpile.

The test took place in January at New Mexico Tech’s Energetic Materials Research & Testing Center (EMRTC) in the hills west of Sandia's Socorro campus. Its purpose was to collect data to validate computer models by simulating a "worst case scenario" of a low-velocity ground impact using a variant of a Davis gun, which was developed during World War I. This is essentially two 16-in (40-cm) gun barrels measuring a total of 40 ft (12 m) pointing in opposite directions. When fired, the mock B61-12 nuclear weapon with a simulated missile body shoots out of one end like in a conventional gun while a 2,000 lb (907 kg) steel reaction mass is ejected from the other end, which absorbs the recoil.

The warhead was fired into an 8-ft (2.4-m) deep, steel-reinforced concrete 10,500 gal (39,746 l) water tank with a soil-filled bunker at the bottom to capture the hardware without damaging the data recorders and other components. Meanwhile, high-speed cameras mounted behind viewports in the tank recorded the impact.

The idea is to use shots with a carefully controlled angle and velocity to simulate a ground impact and test the design margin of the warhead ground fuze's impact sensor response. By carefully calculating the angle and velocity, the team were not only able to control the factors in the experiment, but also assess its success.

"The reaction mass landed just where we expected it to, a first indication that we are close to the velocity we wanted," says lead engineer Tyler Keil.

The test firing was part of National Nuclear Security Administration's (NNSA) US$8.1 billion, 10-year B61-12 Life Extension Program (LEP), which is designed to extend the life of America's existing nuclear arsenal while maintaining its effectiveness and safety. The Sandia team will spend the next year assessing the test data. The results will then be used to improve the warhead design, which will then be subjected to the same test.

"The B61-12 LEP has performed several impact tests of various target types and velocities over the last year to verify its ground fuzing performance," says Keil. "The Davis gun test series specifically tests the B61-12 ground fuzing performance during a water impact. All of the impact testing contributes to how reliably the B61-12 will fuze upon a ground impact."

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