Why the US Military Detonated an Atomic Bomb Off the Coast of California

August 17, 2023Matt Fratus
Atomic Bomb

The spray dome of the Swordfish Trial after a nuclear depth charge detonated in the Pacific Ocean on May 11, 1962. Wikimedia Commons photo.

On May 11, 1962, at approximately 1:02 p.m. Pacific Standard Time, a colossal mushroom cloud erupted from the ocean some 400 nautical miles off the coast of Southern California. The explosion was the result of a nuclear depth charge that had been detonated 650 feet below the ocean’s surface. 

The detonation, overseen by the United States Department of Defense as part of a doomsday program code-named Swordfish, was conducted to evaluate the effectiveness of a new anti-submarine rocket system — the RUR-5 ASROC. Swordfish was one of 36 atomic trials performed as part of the DoD-sponsored Operation Dominic I between April 1962 and November 1962. 

Operation Dominic I was launched after negotiations between the US and the Soviet Union ended with neither side agreeing to suspend nuclear testing.  Most of the 36 trials were conducted to improve various processes for developing or improving nuclear weapons, with the ultimate goal of making them more efficient. Each trial focused on a specific area of concern, such as safety, deployment capabilities, or the lethality of the weapons.

Atomic Bomb, nuke, swordfish

An ASROC (Antisubmarine Rocket) launcher aboard the US Navy guided missile cruiser USS Columbus in 1962. The USS Agerholm was the first US Navy surface ship to shoot an anti-submarine nuclear weapon. Wikimedia Commons photo.

Swordfish had two main objectives. First, the trial would determine whether the RUR-5 ASROC could safely launch a nuclear warhead and hit its target. Second, following the detonation, the radioactive water around the blast site would be used to study the potential effects of radiation on ships, submarines, sonar technology, and personnel.

For the Swordfish trial, the DoD established Joint Task Force 8.9, which included a number of US Navy ships and submarines that would participate in the test. On May 11, 1962, the USS Agerholm, a Gearing-class destroyer equipped with the RUR-5 ASROC, took its position off the coast of California and awaited the order to fire the missile containing the nuclear depth charge. Two Gearing-class destroyers, a Fletcher-class destroyer, and a surfaced submarine were towed within 1 to 2 miles of the target site.

The test began with the Agerholm firing the ASROC at a floating target. The rocket raced through the air and then jettisoned its 10-kiloton nuclear warhead, which was equipped with a parachute. The nuke floated down and splashed into the ocean just 20 yards from the target, sank below the waves, and exploded 40 seconds later. It was the first time a US Navy surface ship had ever successfully fired an anti-submarine nuclear weapon.

Hours after the explosion, US Navy researchers began studying its effects on the vessels anchored within the vicinity of the impact zone. They concluded that the radiation would cause damage to the vessels themselves but not harm their crew members, so long as they remained at least 350 yards away from the detonation site.  

Swordfish and the other atomic trials conducted under Operation Dominic I would ultimately prove crucial to US national security — not so much because of the findings they yielded, but because they represented a significant escalation of force to America’s foreign adversaries. 

In 1963, the US, the United Kingdom, and the Soviet Union — which had also been conducting nuclear testing of their own — signed the Partial Test Ban Treaty. The PTBT required all three signatories to abstain from conducting nuclear weapons tests that would cause radioactive debris underground, underwater, and in outer space environments. As a result, the DoD ceased developing an atomic depth charge. All nuclear warheads were deactivated and taken out of service by 1989.

Read Next: Why the US Navy Annihilated Its Own Battleships With Atomic Bombs

Matt Fratus
Matt Fratus

Matt Fratus is a history staff writer for Coffee or Die. He prides himself on uncovering the most fascinating tales of history by sharing them through any means of engaging storytelling. He writes for his micro-blog @LateNightHistory on Instagram, where he shares the story behind the image. He is also the host of the Late Night History podcast. When not writing about history, Matt enjoys volunteering for One More Wave and rooting for Boston sports teams.

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