On This Day: American submarine USS Thresher sinks, killing 129 seamen

APRIL 10, 1963: One hundred and twenty-nine Americans died in the world’s worst submarine disaster when USS Thresher sank on this day in 1963

The world’s most advanced sub became the first nuclear vessel to be lost at sea while conducting tests 300 miles off the coast of Cape Cod.

The crew revealed their distress in a final radio message to a nearby ship, saying: ‘Minor difficulties, have positive up-angle, attempting to blow’.

A garbled message then followed, with the clearly audible word ‘900’, before the airwaves turned silent.

The Thresher, which had been built only three years earlier, had unexpectedly and suddenly sunk to the seabed 8,400ft below and then imploded under pressure.

The wreckage stretched for more than a mile across the bottom of the Atlantic Ocean in a disaster that left all 16 officers, 96 sailors and 17 civilians on board dead.

‘It was like someone put the submarine in a shredding machine,’ said oceanographer Robert Ballard after using a 1986 survey of the Titanic as cover to view the Thresher.

The crew of the 'USS Preserver' prepare to dive as they attempt to locate  'USS Thresher,' (Getty)

‘It was breathtaking. There were only a couple of parts that looked like a submarine.’

Initially, though, it was thought that the seamen could have escaped the worst, and 15 Navy ships were dispatched to search the area where the sub was lost.

A U.S. News of the Day newsreel shows the search for the Thresher – with sailors examining maps and the fleet scouring the surface.


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Eventually, sonar technology showed that the Thresher had been broken up – with the implosion taking just 0.1 seconds, which is too fast for human nervous systems to feel.

Two days later, President John F Kennedy ordered all flags to be flown at half-mast in honour of the lost submariners and shipyard workers.

It later emerged that a brazed joint on a pipe burst and sprayed seawater onto an electrical panel, shorting it and shutting down the nuclear reactor.

The submarine 'USS Sea Owl' joined the search for the sunken nuclear-powers sub (Getty)

The ‘900’ reference in the final radio message to the USS Skylark is believed to mean that the Thresher was 900ft below its test depth of 1,300ft.

A probe found that the 278ft long submarine, which could travel underwater for unlimited distances due to nuclear propulsion, was actually at 2,400ft when it imploded.

A subsequent inquest found that the cigar-shaped vessel, which had been designed to be quieter and avoid detection, was badly engineered.


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In the aftermath, Admiral Hyman Rickover said: ‘I believe the loss of the Thresher should not be viewed solely as the result of failure of a specific braze, weld, system or component, but rather should be considered a consequence of the philosophy of design, construction and inspection that has been permitted in our naval shipbuilding programmes.

‘I think it is important that we re-evaluate our present practices where, in the desire to make advancements, we may have forsaken the fundamentals of good engineering.’

Yet it would not be the last nuclear submarine to sink in peacetime.

Part of the 'USS Thresher' photographed underwater during a search mission (Getty)

In 1968, another American boat, the USS Scorpion, was lost in the mid-Atlantic after a faulty torpedo returned and hit it.

Both were deeply embarrassing for the United States amid the Cold War.

Four Soviet submarines were also lost, although their disappearances were largely kept secret for three decades.


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One disaster the Russians did not hide was the fate of the K-141 Kursk, which sank in 2000 – killing all 118 men on board – after an explosion in the torpedo compartment.

In 2003, another Russian sub, the K-159, a Soviet-era vessel, sank and killed eight men after being ripped from its moorings during a storm.