Today marks the 50th anniversary of the sinking of the USS Thresher.

At the time Thresher was a super-weapon – one of the main demonstrations of America’s Cold-War technological prowess.  Faster and deeper-diving than any previous class of submarines, with a nuclear power plant giving it effectively-unlimited range, armed with the latest guided torpedos and anti-submarine missiles (including the nuclear-tipped SUBROC), it was the lead ship of what was initially intended to be a class of 14 boats.  It incorporated every lesson that the US had learned about submarine warare in World War 2, and everything they’d learned from the defeated Germans, and from the decade and a half of tete-a-tete up to that point in the Cold War.

The sub left Portsmouth, New Hampshire 50 years ago yesterday for a series of deep dive tests, part of its fleet acceptance trials – so a number of the men onboard were civilian contractors from the Portsmouth Navy Yard.  After a day of trim testing, at about 7:47AM, Thresher began its descent to its “test depth” – which, in submarine terms, is deeper than its “operating depth”, but about half of its estimated “crush depth”.

At an estimated depth of about 1,000 feet, a chain of problems occurred, as reported to the attendant sub rescue ship USS Skylark over the “Gertrude”, an acoustic telephone  (developed before World War 2, and still in service on submarines around the world) that allows voice communications underwater;  a silver-braised thru-hull tube apparently ruptured, spraying high-pressure air all over the engine room…

…which shorted out electrical panels, causing the reactor to “scram”, or shut down.

Navy standard operating procedure was to shut off the steam system, helping prevent overly-rapid cooling of the reactor (which could itself cause catastrophic problems under the wrong circumstances, although over a time frame that wouldn’t have mattered in the Thresher’s case.  

Nuclear submarines don’t usually “blow” their ballast tanks to surface (pump out the water with high-pressure compressed air); they usually rely on their “planes” (think airplane elevator fins) and their engine power to surface.  But with the engine shut off and the engine room getting heavier from the burst pipe, the skipper, Commander John Harvey, ordered a “blow” of the tanks.

Which led to the next link in the catastrophic chain; when compressed air expands, it cools off.  The further and faster the compression drops, the colder the air gets.  Spray a can of compressed-air computer cleaner for a few seconds to test it; it gets cold.  Dropping from 3,000 PSI apparently caused the released air to freeze over the ballast tanks’ outflow valves, preventing the ballast from being blown.

The sub likely sank stern-first, down to about 400 feet below its estimated crush depth of 2,000 feet, before the hull imploded, sending a ram of water through the boat at a speed later estimated at 4,000 miles per hour, ripping the three-inch-thick steel of the boat’s hull to shreds.

The loss of the Thresher – still the worst loss of life in any submarine disaster in history – was a watershed moment in submarine design. At a time when submarines were being built to operate at depths four times greater than during World War 2 – which, let’s remember, was only a decade in the past when Thresher was designed, 15 years when it launched in 1961 – the notion of “quality control” needed a radical upgrade.  The US Navy started its “Sub Safe” program as a result – a relentlessly difficult quality control program that set the standard for intensity of effort and scrutiny of vendors, and may have been one of the most successful government programs in history.

Which has led to a perception that submarines are very safe.  The Thresher disaster garnered massive publicity fifty years ago – and other than the sinking of the USS Scorpion six years later (due apparently to a fire in a torpedo, which led to another safety program of its own), it was the last submarine disaster the US has suffered.

For the past 44 years, submarine disasters are something that happens to other countries; five Soviet and one Russian nuclear submarines have sunk since Thresher‘s loss.

We’ve had some near-misses; a couple of submarines (USS San Francisco and USS Ulysses S. Grant) collided with undersea mountains and suffered massive damage, but returned to port with their crews alive (and their skippers headed for tours commanding radio towers in Nevada) – but nothing like the Thresher, knock wood.

And yet submarine accidents used to be distressingly common, even in the US; Thresher was the 17th of 18 US submarines lost to accidents.

Apropos not much.

This entry was posted by by Mitch Berg on Wednesday, April 10th, 2013 at 1:11 pm and is filed under History And Its Making. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.