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THRESHER: A Disturbing Assessment

The THRESHER UQC (underwater telephone) exchanges with her escort ship, the USS SKYLARK (ASR-20,) and - primarily - the SOSUS (HMCS Shelburne) acoustic data support the conclusion that THRESHER knew that her depth was increasing (going deeper that test depth) 48 seconds after the reactor scrammed at 0909.0R and she lost propulsion. The basis for that conclusion was the detection of a failed
attempt to blow ballast 48s after the primary electrical bus began exhibiting stability anomalies.

Further THRESHER sank from 1300-feet at 0909.0R to collapse at 2400-feet at 0918.4R on 10 April 1963. That's an average sink-rate of
117 ft/min or 1.15 knots. The THRESHER Court of Inquiry erroneously concluded a sea-connected pipe between two and five inches in diameter had burst and the resulting flooding caused loss of propulsion. Such an event would have created impact generated resonances -"screaming" narrowband energy - that would have "insonified" the entire western North Atlantic basin, and no such detection occurred. Further, THRESHER never reported flooding to SKYLARK.

These data support the conclusion that THRESHER was ballasted heavy and held at her depth by speed and the action of her dive planes (slightly on rise)

The question that arises from these assessments is: "Why was THRESHER trimmed heavy when - if she had been trimmed
light and held at depth by action of the dive planes - she would have risen when she lost propulsion, and the disaster would not
have occurred.

A technical exchange site that I monitor and contribute to provided the following comment relative to THRESHER.

The ship operators of the day (1963) tended to ride the ship on its planes–only so instead of holding the ship down as it was positively buoyant, they held it up as they tended to run negatively buoyant.

So, we have that disturbing conclusion: THRESHER was lost because she was out-of-trim (heavy) at test-depth and, when propulsion was lost, her inabilty to blow ballast because of the formation of ice in the air line, caused her sink to collapse at almost twice test depth.





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