[Milsurplus] Loss of the Thresher, 1963

[Hubert Miller]

I am going to quote some to me interesting material from article "SUBSAFE: Legacy of USS Thesher",  'Modern War' magazine, Jan. 2019, p 68 - 71.

"Court of Inquiry found the probable cause of the sinking was a failure of a weld...
With no way to surface, the leaking pipe gradually increased the boat's density, pulling her below the test depth of 1300 feet...
An alternative theory was proposed in 2013 by a Sound Surveillance System ( SOSUS ), the seabed sensors, analyst Bruce Rule...
A decommissioned conventional submarine was intentionally sunk to recreate events central to the Court of Inquiry's findings. At a depth of 1000
feet the hull collapsed. Water entered the hull at the same rate as was indicated by SOSUS recordings of Thresher - 1650 miles an hour...
Rule's primary objection is the lack of detectable ( substantial ) casualty prior to the electrical bus shutdown...

The submarine gave no sign of distress and was cruising at a depth of approximately 1000 feet...
At 09:11 the main electric bus failed shutting down the main coolant pump...Thresher radioed 'experiencing minor difficulty...attempting to blow'.
There was no mention of flooding then or at any other time.
At 09:15 a message to Skylark included the number 900. It generally has been interpreted as referring to 900 feet below her test depth, or 2200 feet.
Both near ( 2400 feet ) and distant ( 1300 NM ) SOSUS sensors recorded the collapse of Thesher's hull and internal components at 09:18."

My question is, what system did the Thresher use to "radio" to the surface ?
-Hue Miller
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