# Cannikin Quake (DD-026)

> On November 6, 1971, the Atomic Energy Commission set off Cannikin 5,875 feet beneath Amchitka Island in Alaska's Aleutians. The test proved the W71 warhead for the Spartan anti-ballistic missile. Its yield was officially 'less than five megatons', making it the largest underground nuclear test the United States has ever conducted. It shook the ground like a magnitude-7 earthquake, lifted the land and nearby seafloor, and caused rockfalls. Seismometers worldwide recorded it. Protests against the test launched the group that became Greenpeace.

- Department: Military (also History)
- First published: 2026-02-08
- Last updated: 2026-02-08
- Permalink: https://detailenjoyer.com/case/cannikin-quake/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## On the timeline

- **Nov. 6, 1971**: Cannikin is detonated 5,875 feet beneath Amchitka Island, Alaska
- **1972**: The protest group becomes the Greenpeace Foundation, and U.S. tests at Amchitka end

Full timeline: https://detailenjoyer.com/timeline/?case=cannikin-quake

## Quick facts

- **DD-026-F01**: Cannikin (1971) was the largest underground nuclear test in U.S. history, with a yield just under five megatons, set off more than a mile beneath Alaska's Amchitka Island. _(Write-up · Exhibit B (America's biggest underground blast))_
- **DD-026-F02**: The protest voyage against Cannikin gave Greenpeace its name and founding mission. _(Write-up · Exhibit G (The birth of Greenpeace))_

## Write-up

America's biggest underground nuke shook the ground like a magnitude 7 quake. Cannikin, Amchitka Island, Alaska, 1971: under 5 megatons, more than a mile down.

1. **When and where**: Cannikin was detonated at 11:00 a.m. Bering Standard Time on November 6, 1971, on Amchitka Island in Alaska's Aleutian chain. It was part of the Atomic Energy Commission's Operation Grommet test series.
2. **America's biggest underground blast**: The official yield was 'less than five megatons', with published estimates ranging from about 4.4 to 5.2 Mt. No larger underground nuclear test has been conducted by the United States.
3. **A warhead for missile defense**: The test proved Livermore's W71 warhead for the Spartan interceptor, the upper tier of the Safeguard anti-ballistic missile system. Spartan was meant to destroy incoming warheads above the atmosphere with a burst of X-rays.
4. **More than a mile down**: The device was emplaced 5,875 feet underground at the bottom of a record-setting shaft about 6,150 feet deep. It was fired from a control point 23 miles away.
5. **Magnitude-7 shaking, worldwide**: Livermore says the blast produced the ground motion of a magnitude-7.0 earthquake. Readings from 43 stations in the Worldwide Standard Seismometer Network gave a body-wave magnitude of 6.8 and a surface-wave magnitude of 5.7.
6. **What it did to the island**: Hundreds of small aftershocks ended when the explosion cavity collapsed 38 hours later, leaving a subsided area where a new lake formed. The seafloor rose by up to about 56 cm nearby. Rockfalls and turf slides covered about 35,000 square feet. The feared tsunami never happened.
7. **The birth of Greenpeace**: Vancouver's Don't Make a Wave Committee sailed the fishing boat Phyllis Cormack, renamed Greenpeace, toward Amchitka to protest the test, but was turned back. In 1972 the group became the Greenpeace Foundation, and the United States ended its tests at Amchitka.

## Related case files

- [Atomic Annie (DD-004)](https://detailenjoyer.com/case/atomic-annie/): Both are U.S. nuclear tests: Atomic Annie's above-ground 1953 artillery shot versus Cannikin's 1971 underground megaton blast.
- [Supersonic Striker (DD-036)](https://detailenjoyer.com/case/supersonic-striker/): The nuclear-deterrence era the B-1 was built for.
- [Gas Blasting (DD-070)](https://detailenjoyer.com/case/gas-blasting/): A far larger underground blast: the largest underground nuclear test the U.S. has conducted.

## Reel vs. record

- **Confirmed from the frames**: the Reel is about the Cannikin test (caption at 0.9 s: 'The Cannikin Test'). Date, place, U.S. underground record and Spartan purpose are all correct. [AEC D+30 report; LLNL; Wikipedia]
- **Precision**: 'nearly five megatons' matches the official 'less than five megatons'. Estimates range from 4.4 to 5.2 Mt. [AEC D+30 report; BSSA 1972; Wikipedia]
- **Overstated**: 'triggering earthquakes'. The AEC reported that 'no large earthquake was triggered'. The blast itself registered like a magnitude 6.8–7.0 event, and what followed were hundreds of small events (mostly below magnitude 4) tied to cavity collapse and minor local fault slip. [AEC D+30 report; Engdahl, BSSA 1972; LLNL]
- **Clarification**: the 'landslides' were local rockfalls, cliff spalling and turf slides on the island, totaling about 35,000 sq ft. No tsunami resulted. [AEC D+30 report; Wikipedia]
- **Confirmed**: 'detected by seismic instruments around the world'. The AEC report cites 43 stations of the Worldwide Standard Seismometer Network. [AEC D+30 report]

## Video: Cannikin Quake: America's Biggest Underground Nuke Shook the Ground Like a Magnitude 7 Quake

- Duration: 25.8 s · Published: 2026-02-08
- File: https://detailenjoyer.com/assets/videos/DUgWTX6EQW9.mp4

### Transcript

DID YOU KNOW? The Cannikin Test was an underground nuclear detonation conducted by the United States on November 6th, 1971, on Amchitka island in Alaska. With a yield of nearly five megatons, it was the largest underground nuclear test ever performed by the U.S. and was intended to test the Spartan anti-ballistic missile warhead. The explosion caused significant ground shock, triggering earthquakes, surface uplift, and landslides. It was detected by seismic instruments around the world. NOW YOU KNOW!

## Questions & answers

**Q: Where was the Cannikin test conducted?**  
A: Cannikin was fired beneath Amchitka Island in the Aleutians on November 6, 1971. _(Source: Write-up · Exhibit A (When and where) · Project CANNIKIN D+30 Day Report: Preliminary Operational and Test Results Summary (AEC, via OSTI); At the Frontier of Missile Defense, 1971 (Lawrence Livermore National Laboratory history); Cannikin (Wikipedia))_

**Q: What was Cannikin's approximate yield?**  
A: The official yield was 'less than five megatons', the largest U.S. underground test. _(Source: Write-up · Exhibit B (America's biggest underground blast) · Project CANNIKIN D+30 Day Report: Preliminary Operational and Test Results Summary (AEC, via OSTI); Seismic effects of the MILROW and CANNIKIN nuclear explosions (Engdahl, BSSA, 1972); Cannikin (Wikipedia))_

**Q: Which weapon's warhead was Cannikin testing?**  
A: It proved the W71 warhead for the Spartan ABM interceptor. _(Source: Write-up · Exhibit C (A warhead for missile defense) · At the Frontier of Missile Defense, 1971 (Lawrence Livermore National Laboratory history); Cannikin (Wikipedia))_

**Q: How strong was the ground motion it produced?**  
A: Livermore says it produced the ground motion of a magnitude-7.0 earthquake. Worldwide stations measured body-wave magnitude 6.8. _(Source: Write-up · Exhibit E (Magnitude-7 shaking, worldwide) · Project CANNIKIN D+30 Day Report: Preliminary Operational and Test Results Summary (AEC, via OSTI); At the Frontier of Missile Defense, 1971 (Lawrence Livermore National Laboratory history))_

**Q: Which organization grew out of protests against Cannikin?**  
A: The Don't Make a Wave Committee's protest boat was named Greenpeace, and the group took the name in 1972. _(Source: Write-up · Exhibit G (The birth of Greenpeace) · Our history (Greenpeace USA); Don't Make a Wave Committee (Wikipedia))_

## Sources

- [Project CANNIKIN D+30 Day Report: Preliminary Operational and Test Results Summary (AEC, via OSTI)](https://doi.org/10.2172/4701483)
- [At the Frontier of Missile Defense, 1971 (Lawrence Livermore National Laboratory history)](https://www.llnl.gov/sites/www/files/1971.pdf)
- [Seismic effects of the MILROW and CANNIKIN nuclear explosions (Engdahl, BSSA, 1972)](https://doi.org/10.1785/bssa0620061411)
- [Long-period water-wave measurements for the MILROW and CANNIKIN nuclear explosions (BSSA, 1972)](https://doi.org/10.1785/bssa0620061559)
- [Cannikin (Wikipedia)](https://en.wikipedia.org/wiki/Cannikin)
- [Our history (Greenpeace USA)](https://www.greenpeace.org/usa/our-history/)
- [Don't Make a Wave Committee (Wikipedia)](https://en.wikipedia.org/wiki/Don't_Make_a_Wave_Committee)

## Cite this case file

Easterling, Marcus. "Cannikin Quake." The Detail Department (DetailEnjoyer), case file DD-026, last updated Feb 8, 2026. https://detailenjoyer.com/case/cannikin-quake/