50 years ago today, the United States conducted its largest-ever underground nuclear test. A Spartan antiballistic missile carrying a W71 warhead was lowered into a 7-foot-wide, 5,873-foot-deep shaft beneath Amchitka Island, Alaska, and detonated. The yield was about 5 Megatons. 
The test went ahead only hours after the Supreme Court refused requests to delay it over the Nixon administration’s failure to issue a comprehensive environmental impact statement. Instead, the court agreed with the admin’s claim any delay would upset the “balance of deterrence.”
Here is some remarkable official footage of the preparations for and results of that huge test. I have watched a lot of nuclear test films over the years, and even though Cannikin was entirely underground, this one never fails to send chills down my spine.
The explosion raised the ground above the shaft 25 feet (it later collapsed into an almost mile-wide, 60-foot-deep subsidence crater). Then-AEC chairman James Schlesinger brought his wife and two daughters to watch. “It was kind of like a train ride,” said nine‐year‐old Emily.
The massive shockwave killed an estimated 900-1,100 sea otters, in some cases crushing their skulls. Other marine mammals died when their lungs ruptured or their eyes were blown out. Thousands of shore birds were killed, their legs pushed through their bodies and spines snapped.
Many men who excavated the shafts for Cannikin and two earlier tests—Long Shot, on Oct. 29, 1965, and Milrow on Oct. 2, 1969—or did other work on Amchitka, sometimes years later, have suffered or died from cancers they blame on radiation from the tests. adn.com/opinions/2017/…
As of January 2017, under the Energy Employees Occupational Illness Compensation Act, the government had “paid 635 Amchitka workers a total of $88.8 million plus $11.9 million in medical costs.” One was Phillip Moreno, a barber and cook who died shortly after being compensated.
In 2019, a Department of Energy official said that the most recent round of environmental samples taken at the sites of the three nuclear tests conducted at Amchitka showed no leaks of radioactive material or “excessive risk.” apnews.com/article/scienc…
A total of 30 Spartan and 70 Sprint ABMs (armed with 1-kt W66 enhanced radiation warheads) were deployed at the Stanley R. Mickelsen Safeguard Complex at Nekoma, North Dakota, to protect 150 Minuteman III ICBMs. The site was only fully operational from Oct. 1975 to Jan. 1976.
The W71 moved to the inactive stockpile in 1976 after Safeguard shut down but was only retired in 1992 and fully dismantled in 1995. To maximize warhead-killing X-rays, its thermonuclear secondary was surrounded by a layer of gold, leading a DOE official to call it a “gold mine.”
Well if that's true, we blew it—literally.
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