U.S. tested its largest hydrogen bomb warhead in 1971

On November 6, 1971, the United States conducted its largest underground hydrogen bomb test-code-named Cannikin-on Amchitka Island in Alaska's Aleutian chain, unleashing a seismic event that reverberated through science, politics, and environmental activism.

The Cannikin test, part of the Operation Grommet series, was designed to evaluate the W71 warhead for the LIM-49 Spartan anti-ballistic missile system. With an explosive yield of nearly 5 megatons of TNT, it remains the most powerful underground nuclear detonation ever carried out by the United States.

Strategic Purpose: A Warhead for Missile Defense

Cannikin was not a weapon of war, but a test of a warhead intended for defense. The W71 warhead was engineered to intercept incoming nuclear missiles as part of the U.S. Safeguard Program-a Cold War-era initiative to shield American cities from Soviet attack. The test aimed to validate the warhead's reliability and performance under extreme conditions.

The device was lowered more than a mile underground into a specially drilled shaft on Amchitka Island, a remote and rugged outpost in the Aleutians. The location was chosen for its isolation and geological stability, though concerns about seismic risks and environmental damage loomed large.

The Blast: Earthquake-Level Shockwaves

At approximately 11:00 a.m. local time, the detonation shook Amchitka with the force of a 7.0 magnitude earthquake, triggering landslides and creating a dome-like bulge on the surface above the test shaft. The explosion vaporized the test chamber and caused measurable ground motion across the region.

Despite the massive energy release, the test was deemed a technical success. The warhead performed as expected, and containment protocols prevented radioactive leakage into the atmosphere. However, the environmental and political fallout was far from contained.

Controversy and Protest: The Birth of Greenpeace

Cannikin became a flashpoint for environmental activism. Scientists and conservationists warned of potential earthquakes, tsunamis, and radioactive contamination. Legal challenges reached the U.S. Supreme Court, which narrowly allowed the test to proceed.

Public opposition was fierce. Among the protestors were members of the newly formed Don't Make a Wave Committee, which would later evolve into Greenpeace. Their efforts to halt the test marked one of the earliest and most visible campaigns of the modern environmental movement.

Legacy: A Test That Echoes Through Time

Though Cannikin did not cause the catastrophic environmental damage feared by some, it left a lasting imprint. Amchitka Island remained off-limits for decades due to contamination concerns, and the test became a symbol of Cold War excess and the risks of unchecked nuclear experimentation.

The Safeguard Program itself was short-lived. By 1976, it was dismantled, and the W71 warhead was retired. Yet the Cannikin test endures as a powerful reminder of the tensions between national security, scientific ambition, and environmental stewardship.

Sources:

• Cannikin - Wikipedia

• Cannikin: The Nuclear Bomb that Split an Island in Two

• 1971 Cannikin - Lawrence Livermore National Laboratory