The Sinking of USS Thresher (SSN-593)

“Experiencing Minor Difficulties”: A Chilling Morning at Sea

The dawn of April 10, 1963, came quietly to Portsmouth Naval Shipyard. Pale light pressed through thin fog over the Piscataqua River, casting long shadows on the silent figures dotting the docks. There had been a buzz of activity barely forty-eight hours earlier—the USS Thresher, the Navy’s pride and promise, had slipped out for another round of sea trials, her crew and a complement of civilian experts eager to prove she was as good as the engineers claimed. Now, those left behind stood idle, watching the horizon with a tension that needed no words.

Roughly two hundred miles east, in the cold black waters of the North Atlantic, the Thresher and her crew of 129 men were descending far deeper than almost any submarine had gone before. No one yet knew that within hours, moments really, the United States would face its worst submarine disaster—a tragedy born not of war, but of physics, engineering, and the hidden, lethal complexity locked inside the hull of a nuclear sub.

Thresher’s Short Brilliant Life

“Lead boat of her class.” Among submariners, that’s a phrase with equal parts pride and pressure. The USS Thresher, hull number SSN-593, was both marvel and mystery when she launched in 1960. Faster, quieter, diving deeper—every inch designed to outsmart Soviet hulls and missiles. She could race underwater at classified speeds, slip undetected with advanced sonar, and strike hard with torpedoes. When she was commissioned in August 1961, she was the most sophisticated submarine on Earth.

After initial months at sea—testing, training, learning her eccentricities—Thresher returned to Portsmouth in mid-1962 for what the Navy called “Post-Shakedown Availability.” The term sounded routine, but the stakes weren’t: repair anything lingering, reinforce systems, upgrade where progress allowed. It ended after a long, meticulous overhaul in early April 1963. She was ready, Navy command said, for one last battery of deep-dive tests before active patrols resumed for real.

Her crew believed it. Most sailors did. But behind the pride was a hard reality: in 1963, military submarines were evolving faster than procedures and quality assurance could keep up. There was no standardized, mandatory safety program like SUBSAFE yet—no bulletproof paper trail to guarantee every weld, every valve, every foot of pipe was ready for what the ocean could throw at it.

Final Preparations and Descent

April 9, 1963. Equipment checks lined up one by one as Thresher and her companion ship, the USS Skylark, prepared for sea. Skylark wasn’t glamorous—she was a submarine rescue ship, designed to shadow subs on risky dives, ready to help in an emergency.

Early the next morning, Thresher slid beneath the waves with a full roster: 112 sailors and 17 civilian technicians—engineers, inspectors, men whose lives were spent pushing boundaries underwater. The plan was methodical: travel out, test systems on the surface, and then descend, step by careful step, to “test depth”—the maximum below which something vital might give.

At 7:47 am, Thresher reported in. She was beginning her descent. The crew maintained regular communication with Skylark, checking off system after system, depth after depth.

By just after 9:00 am, the sub was below 1,000 feet. All signs, at least outwardly, remained normal.

Catastrophe Unfolds

At exactly 9:13 am, Skylark received a message from the deep. Parts of it were garbled by seawater and static, but what got through carried an unmistakable urgency: “Experiencing minor difficulties. Have positive up-angle. Attempting to blow.”

In submarine language, these are red flags. A positive up-angle meant the submarine’s nose was pointed toward the surface—likely a desperate attempt to rise. Attempting to “blow” referred to blasting compressed air into the ballast tanks—an emergency procedure designed to force water out, make the sub buoyant, and break for safety above.

A minute later, the messages came through even more broken, almost unintelligible. Just fragments: “... test depth ... blow …” And then, at 9:18 am, only silence. No more words. No more signals from 8,000 feet below.

Skylark followed procedure, deploying rescue buoys, sending coded pings into the ocean. Hope was thin—the Thresher was built so strong that if she had sunk below a certain depth, rescue was impossible. But for a few surreal hours, the Navy held out. Maybe equipment had failed. Maybe the crew was alive, fighting. Ships and planes converged. An oil slick was spotted. Bits of debris floated to the surface—a chunk of insulation, a torn scrap of metal.

There would be no survivors.

Shock Waves and Sorrow

Within hours, word spread. The Pentagon notified families. Six wives waiting at the shipyard fainted when the news became clear. The country was glued to television and radio. How could such a thing happen in peacetime, with the world’s best engineers and technology?

All 129 souls aboard Thresher were lost—the most deaths in a single American submarine disaster, then or since. Some were seasoned sailors. Some were young men on their first tour. The civilians included engineers fiercely proud of their work. Chief Electrician’s Mate Thomas E. Dee left behind a wife and four children. Commander John W. Harvey, the submarine’s captain, was the grandson of a Navy admiral—a legacy ending in black water.

At the Portsmouth pier, the mood became funereal. Maintenance logs stacked near the bollards told their own silent story—questions no one could answer yet. Even hardened machinists cried. At the sub school, instructors pulled aside chandeliers and flags, working quietly, trying to offer explanations to bewildered students.

Engineering, Failure, and Fate

The investigation took months, stretching from the shattered families to the highest levels of military command. The Navy’s Court of Inquiry reviewed every available trace. Wreckage analysis would later be led by the deep-diving bathyscaphe Trieste, which in June 1963 found Thresher’s remains in a field of twisted steel more than a mile and a half beneath the waves.

There was no simple, single cause. The likeliest scenario, pieced together from testimony and engineering logic, haunted Navy planners:

• A Silver-Brazed Joint Fails: In the engine room, a critical pipe joint—holding back thousands of pounds of seawater—failed. Seawater began to pour in. The location was deep in the sub, where access in an emergency is tough and time is short.

• Propulsion Lost: The flooding led to an electrical short, shutting down the main engine. Without power, the sub couldn’t drive itself upward.

• An Emergency That Wouldn’t Answer: The crew tried to blow the ballast tanks—one last card to play. But in the cold, humid depths, the compressed air lines contained moisture. Ice formed as the air was released, blocking the pipes. The tanks wouldn’t clear, and Thresher, already heavy from flooding, couldn’t rise.

Down she went, the hull collapsing violently as it crushed under increasing pressure—an end as swift as it was final.

SUBSAFE

There was anger, too. Congressional hearings followed, as well as public outcry. How could such a vessel, built at enormous expense and blessed with so many experts, fail so suddenly?

The U.S. Navy’s answer was not just words, but a complete overhaul. They created one of the strictest quality-control and safety standards in military history: the SUBSAFE program. Every submarine that went to sea after Thresher would be built, inspected, and maintained to standards that allowed for no guesswork, no shortcuts. Every weld, every valve, every system that controlled flooding or buoyancy had to have a documented life story—no exceptions.

It cost millions, even billions, over the years. There were delays, setbacks. But not one American submarine certified under SUBSAFE has ever been lost at sea.

Memory in Steel and Saltwater

Today, six decades after the morning Thresher slipped away, there’s a memorial at Portsmouth—a simple sail and a plaque, surrounded by names and fresh-cut flowers left by the old crew’s children and grandchildren. Each April, Navy officers gather, hats in hand, to remember what was lost and what was gained.

The Thresher disaster is still part of every submariner’s education. It is recounted not as blame, but as a warning and a promise: complexity demands humility. Trust, but verify. And when working at the limits—the edge of pressure, metal, and the unexpected—you respect the ocean.

For the families, the pain endures. They live with uncertainty: what exactly did their husbands, fathers, sons see or feel in those last minutes? Few details exist. But if there is any comfort, it lies in this—what was learned from Thresher has saved countless lives, making today’s silent service safer than her pioneers ever could have hoped.

And on quiet mornings by the pier, when the mist is low and the river smooth, you can almost hear the hum of submarine machinery beneath the surface—a promise, and a memory, forever bound up in the steel and silence of the deep.