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A submarine accident (thread) is never great. To give an idea, I’ll try to give a feel for what it’s like onboard when the worst happens. This was the USS Thresher on 10th April 1963. She was a cutting edge American hunter killer, conducting test dives after refit. 1/18
The procedure was standard. Slow circles descending depth under USS Skylark, a submarine rescue ship. At each stop, compartments would check fore to aft for signs of water ingress into the hull. 2/18
The aim was to go to 1000 feet, her accredited test depth, to certify her hull integrity.
At about 0809 hrs, Thresher reaches test depth. She retains communication with Skylark via her underwater telephone (Gertrude) and is slowing turning. That’s when it happens.
3/18
At about 0809 hrs, Thresher reaches test depth. She retains communication with Skylark via her underwater telephone (Gertrude) and is slowing turning. That’s when it happens.
3/18
The bang as a pipe fractures would have been heard throughout the boat. Seawater flooded in under enormous pressure and instantly formed a dense mist, pouring in tonnes a minute. The roar would have been deafening. In the main control room,
4/18
4/18
and machinery control room, alarm bells and buzzers would have sounded and lights flashed.
A team would have instantly tried to slow the flood as any watertight doors not already closed were slammed shut. If the pipe was behind panelling then the lads
5/18
A team would have instantly tried to slow the flood as any watertight doors not already closed were slammed shut. If the pipe was behind panelling then the lads
5/18
would have used whatever they could to smash their way in to access the fracture. The water would have been ankle deep in seconds, the spray making it hard to breathe, and the water under so much pressure it would have been pain simply to touch.
6/18
6/18
In the control room the captain, Lt Cdr John Wesley Harvey, would have in seconds, faced his nightmare. We can assume he ordered planes full up, blow main ballast, and rung on maximum speed to the engine room. He knew it was a race to get Thresher
7/18
7/18
shallow or even better, on the surface. There would have been concern but submariners train for the worst and Threshers ships company would have responded quickly and efficiently.
We will never really know why, but when she tried to get air in the ballast tanks,
8/18
We will never really know why, but when she tried to get air in the ballast tanks,
8/18
something went wrong. Ice crystals forming in the tanks as the air cools may have clogged temporary yard putting on protective valves not removed prior to sailing was one theory.
Threshers tanks fail to blow fully.
9/18
Threshers tanks fail to blow fully.
9/18
Despite the roar of the flood aft and the hiss as air is blown into the tanks, Thresher maintains communications with Sklark.
0913 hrs:-“[We are] experiencing minor difficulty, have positive up-angle, attempting to blow."
10/18
0913 hrs:-“[We are] experiencing minor difficulty, have positive up-angle, attempting to blow."
10/18
Down aft the damage control teams are frantically trying to stem the flood. Hatches closed, they were trapped, probably chest deep in freezing water. In the control room it becomes clear ballast tanks are not blowing and flooding aft, Thresher begins to lose depth control.
11/18
11/18
It is at this stage it is assumed that water created a machinery breakdown and the reactor automatically scrammed or shut down. The captain would have ordered change over to battery propulsion but Thresher, stern all but flooded, decends quickly.
12/18
12/18
Loss of power will have sent more alarms off. Main lighting gone, she’d have been lit by emergency battle lamps. Throughout the hull terrified ships company would have grabbed anything fixed as the hull assumed a steeper descent angle.
13/18
13/18
Unsecured gear and people will have fallen aft.
We can be sure that even now the Skipper would have tried everything he knew to get her level. Her engineering team will have frantically gone through the reactor re-start sequence. But that needed minutes.
14/18
We can be sure that even now the Skipper would have tried everything he knew to get her level. Her engineering team will have frantically gone through the reactor re-start sequence. But that needed minutes.
14/18
And Thresher didn’t have minutes.
As the boat descended there would have been shrieks and groans as she passed crush depth. In the semi darkness blokes would have been making their final peace. The hull would have shaken.
15/18
As the boat descended there would have been shrieks and groans as she passed crush depth. In the semi darkness blokes would have been making their final peace. The hull would have shaken.
15/18
There might have been a last despairing blow of air into tanks and her prop will have thrashed as it tried to get her to the surface.
At 0917 hrs:-“ "exceeding test depth ...”
16/18
At 0917 hrs:-“ "exceeding test depth ...”
16/18
The end would have been mercifully quick. At 0918 hrs, with thousands of pounds of pressure per foot, her hull would have given way in a tenth of a second. Too quick for the human brain to even comprehend. Thresher was crushed aft of the sail and flooded completely forward
17/18
17/18
and sank to the bottom. Sixteen officers and ninety six other ranks went with her.
That’s why if you were in the RN, no matter what the nationality, a SUBMISS /SUBSUNK signal is never joked about.
I pray for a happy outcome with the
53, but IAH it’s not looking good. 
That’s why if you were in the RN, no matter what the nationality, a SUBMISS /SUBSUNK signal is never joked about.
I pray for a happy outcome with the
53, but IAH it’s not looking good.
