Since the end of World War II, the United States has lost only two submarines: USS Thresher and USS Scorpion. Scorpion was the last American submarine to leave on patrol and never come back.

Scorpion, her nuclear power plant, and two onboard nuclear weapons were never recovered. They remain on the bottom of the Atlantic Ocean, roughly 400 miles southwest of the Azores. The Navy has never fully explained the loss of the submarine and its 99 crew members.

That has left Scorpion in a strange place in American naval history: officially unresolved, heavily studied, and still argued over by people who know the submarine world well.

A Nuclear Sub Built for Speed

USS Scorpion was a Skipjack-class nuclear-powered attack submarine. Scorpion and those of her class were part of a new generation of submarines designed for greater speed underwater than on the surface. The use of nuclear power over traditional diesel engines allowed the submarine to spend almost all of its time fully submerged instead of cruising on the surface and submerging near enemy waters. This, in turn, meant that the teardrop-shaped hull was streamlined for underwater travel rather than for surface travel.

As a result of this streamlining, Skipjack subs could hit speeds of 33 knots underwater. This made Scorpion one-third faster than the Skate-class subs, an earlier class of nuclear-powered submarines that used a more conventional hull layout. Scorpion was powered by a single Westinghouse S5W nuclear reactor generating 11,000 kilowatts. It displaced 3,000 tons underwater, and was 251 feet long. The sub was fitted with six 533-millimeter torpedo tubes and carried a mix of both anti-surface and anti-submarine weapons.

An Espionage Mission Gone Wrong

On May 20, 1968, the U.S. Navy ordered one of her fastest submarines, the USS Scorpion, to conduct a high-tech espionage mission. The submarine, fresh off maneuvers with the Sixth Fleet in the Mediterranean Sea, was diverted to intercept a Soviet naval task force located southwest of the Canary Islands. Consisting of an Echo-II-class diesel-electric submarine, a destroyer, a submarine rescue vessel, two hydrographic survey ships, and an oiler, the task force was thought to be conducting an intelligence operation of its own, measuring the acoustic signatures of NATO warships in the region.

Scorpion was ideally suited for the task. What better to stalk the Soviet spy task force than a submarine designed to avoid detection? On May 21, the submarine checked in via radio, reporting its position as 250 miles southwest of the Azores, estimating it would return from the mission on May 27.

But Scorpion would never be heard from again.

Three Theories, Zero Conclusions

By May 24, Vice Admiral Arnold Schade, Commander of the Atlantic Submarine Fleet, knew the submarine had failed to respond to classified communications messages, but the Navy waited until May 27 to officially declare her missing. Within hours, the service discovered the Sound Surveillance System (SOSUS)—an underwater network designed to detect the acoustic signatures of Soviet submarines—had detected the breakup of the Scorpion’s hull as she descended, mortally stricken, beyond her hull’s crush depth.

The standard public account says Scorpion was found on October 28, 1968, in roughly 11,000 feet of water, approximately 400 miles southwest of the Azores. None of the 99 crew members survived.

A Navy inquiry did not produce a definitive public answer. Still, the torpedo theory has more weight in the current public record than the original story made clear. A Navy Memorial summary says the court of inquiry could not reach a definitive conclusion, but that “a torpedo accident was considered to be the most likely scenario.” Under that theory, Scorpion may have suffered a “hot run” torpedo—a weapon that became active while still in its tube. The submarine’s reported turn away from its expected course has often been cited as a clue, because one response to a running torpedo was to turn away and try to trigger its anti-friendly-fire mechanism.

Other explanations have centered on a mechanical casualty or an internal explosion. One version starts with Scorpion’s Trash Disposal Unit, or TDU, which allowed the crew to dispose of waste at sea. Scorpion had a reputation for mechanical trouble—some sailors privately called it “Scrapiron”—and the TDU had been associated with flooding issues before. In this theory, a failed TDU could have let seawater into the submarine, with the water eventually reaching the 69-ton lead-acid battery and causing a short or explosion.

A related battery-well theory points to hydrogen gas. Submarine batteries can generate hydrogen while charging, and hydrogen is a nasty problem inside a sealed steel pressure hull: colorless, odorless, and dangerous if it accumulates. A spark in the wrong place could have ignited the gas and produced a violent internal explosion.

Another argument has grown louder in recent years. In a 2025 Naval History article, author Ed Offley argued that the familiar Scorpion narrative leaves out too much of the internal Navy record. His reading of declassified Court of Inquiry material points to a possible “large charge weight external to the pressure hull,” and he argues that logs, witness accounts, and search-ship capabilities suggest the wreck may have been effectively located in early June 1968 rather than first found in late October.

That’s not the Navy’s adopted public conclusion, but a contested theory, and it has been pushed back on by other submarine and naval-history specialists.

The Nuclear Wreck on the Seafloor

Scorpion also took its nuclear reactor and two nuclear-tipped MK-45 ASTOR anti-submarine torpedoes to the bottom. The reactor and the torpedoes were never recovered.

That sounds like the beginning of a different disaster, but the official environmental record is calmer than the image suggests. The latest publicly available Naval Nuclear Propulsion Program environmental reporting says follow-up sampling near the Scorpion site in 1979, 1986, and 1998 found no evidence of radioactivity released from the reactor fuel elements. The report also says the 1986 and 1998 sampling campaigns specifically assessed the nuclear torpedoes for plutonium leakage, and that the measured plutonium levels were consistent with background fallout from weapons testing, not leakage from Scorpion’s weapons. The report’s bottom line: the wreck has had “no discernible effect on the radioactivity in the environment.”

The U.S. Navy made sweeping changes to its submarine fleet after the prior loss of USS Thresher in 1963. A new program, SUBSAFE, ensured that submarines were built with safety-first principles, including the ability for a stricken sub to surface under any conditions. While Scorpion had not been built under the SUBSAFE program, successive generations of submarines have been built to exacting program standards. Two such submarines, San Francisco and Connecticut, have survived major collisions with underwater mountains, allowing them to surface and even return to port under their own power.

USS Scorpion’s sinking was a tragedy that reinforced the need for absolute safety aboard Navy submarines. The loss of 99 lives and two nuclear weapons was a deadly rebuke to substandard practices, and helped transform the undersea Navy. We may never know what happened to Scorpion, but we do know that if it happens again, a submarine and her crew will almost certainly return home.