US largest underground nuke tests


Lorenzo von Matterhorn
Jan 31, 2009
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The Faultless Site

Operation Crosstie - Faultless

The Faultless test was a calibration test conducted in a mine cavity 3,200 feet beneath the Hot Creek Valley near Tonopah, Nevada, with a yield of around 1 megaton. This test was conducted to see if the land was fit for testing a 5 megaton thermonuclear warhead for the Spartan missile.[5] The test failed because of the large degree of faulting that resulted in the area around the test. It was decided that the land was unfit for multi-megaton nuclear tests, so a similar calibration test was conducted at Amchitka Island, Alaska, in the fall of 1969 during Operation Mandrel.

The 7.4 foot diameter steel pipe that was used to place the bomb remains at the test site. The top of the pipe was originally flush with the surface, however, the ground sunk by nine feet following the explosion.[6] A plaque is mounted on the exposed pipe to commemorate the event.


The W-71 nuclear warhead was a US thermonuclear warhead developed at Lawrence Livermore National Laboratory in California and deployed on the LIM-49A Spartan missile, a component of the Safeguard Program, an anti-ballistic missile (ABM) defense system briefly deployed by the US in the 1970s.

The W-71 warhead was designed to intercept incoming enemy warheads at long range, as far as 450 miles (720 km) from the launch point. The interception took place at such high altitudes, comparable to low earth orbit, where there is practically no air. At these altitudes, x-rays resulting from the nuclear explosion can destroy incoming reentry vehicles at distances on the order of 10 miles (16 km), which made the problem of guiding the missile to the required accuracies much simpler than earlier designs that had lethal ranges of less than 1,000 feet (300 m).[1]

The W-71 warhead had a yield of around 5 megatons of TNT (21 PJ). The warhead package was roughly a cylinder, 42 inches (1.1 m) in diameter and 101 inches (2.6 m) long. The complete warhead weighed around 2,850 pounds (1,290 kg).[2]

The W71 produced great amounts of x-rays, and needed to minimize fission output and debris to reduce the radar blackout effect that fission products and debris produce on anti-ballistic missile radar systems.[1][3]



Operation Grommet - Cannikin

Cannikin was an underground nuclear weapons test performed on November 6, 1971, on Amchitka island, Alaska, by the United States Atomic Energy Commission.[1] The experiment, part of the Operation Grommet nuclear test series, tested the unique W71 warhead design for the LIM-49 Spartan anti-ballistic missile.[2] With an explosive yield of almost 5 megatons of TNT (21 PJ), the test was the largest underground explosion ever detonated by the United States.[3]

Prior to the main five-megaton test in 1971, a 1 Mt (4.2 PJ) test took place on the island on October 2, 1969, for calibration purposes, and to ensure the subsequent Cannikin test could be contained.[3] This test, Milrow, was included in the Operation Mandrel nuclear test series.

Preparation for the test took place over five years and involved hundreds of staff from the Lawrence Radiation Laboratory, later the Lawrence Livermore National Laboratory. Drilling for the shaft for the Milrow test began in March 1967, with drilling for the Cannikin test commencing in August 1967.[5]

To perform the test, 400 tons of equipment was placed in a shaft 1,870 metres (6,150 ft) deep and 2.3 metres (90 in) wide. Test support equipment was designed to survive a ground upheaval of 4.6 metres (15 ft) at test time.[2]

Cannikin Test - caused 6.8 magnitude earthquake - 1000 aftershocks up to 4.0 magnitude over the next 30 days