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Retrospective on the Loss of the ARA SAN JUAN (S-42)

This posting provides what those who - in the future - may be concerned with analyses of acoustic detections of submarine collapse events should “take away” from the ARA SAN JUAN event.

Almost all one needed to know about the loss of the ARA SAN JUAN on 15 Nov 2017 was provided by the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO) Report of 29 Nov 2017, e.g., approximate position, event time, depth, energy yield, and duration of the collapse of the SAN JUAN pressure-hull.

Most of this information was not directly provided by the CTBTO Report but could be derived from discussions in the Report of the acoustic signal that was time- and position-correlated with the loss of the SAN JUAN.

Why then did the CTBTO Report not provide this information? Based on discussions with that organization, it appears they consider their mission to be the reporting of events and not assessments of the cause of such events.

Basically, the detection of the SAN JUAN associated acoustic signal with a 40-50 dB signal-to-noise ratio at a range of 3261 nautical miles (nm) eliminated all possible sources other than collapse of the pressure-hull at extreme depth.

Based on the signal level and depth and energy yield calculations derived from images of the CTBTO detections in the Report, the writer responded to a request from public news sources for a statement which was: the SAN JUAN collapsed at great depth in about 40 milliseconds (ms) (later revised to 35ms), faster than the minimum human cognitive reaction time of 80-100ms. No one drown nor did they experience any pain; death was instantaneous at 1351 GMT on 15 Nov, about three hours after the last SAN JUAN radio transmission.

The Argentine Navy acknowledged receipt of that assessment via “social media” but did not – as appropriate – provide further comment. After all, the report had come from an unknown source who had been employed by the US Office of Naval Intelligence (ONI). Most of the press coverage - which included French, British and German outlets - attributed the report to ONI.

The unique feature of the SAN JUAN acoustic event was the collapse event echo pattern which involved not only 11 reflected signals paths from bathymetric features remote by hundreds of nm to the event position but also reflections from features within less than 800m of the collapse site. All these reflections were detected by the CTBTO hydrophone at Ascension Island at a direct range of 3261 nm.

Identification of the near-field reflections confirmed – before the wreck was located – that collapse had occurred above a convoluted bathymetry consistent with an undersea canyon.

It is suggested that those activities that might be concerned with any future submarine loss event that involves collapse obtain either the CTBTO acoustic data or any available US acoustic data on the SAN JUAN to conduct a very high time-resolution analysis of the near-field reflected signals for comparison with the known bathymetry of the wreck-site to gain knowledge of the dimensions and forms of the involved reflecting surfaces.

None of the other six collapse events analyzed by the writer included near-field reflected signals primarily because these events occurred above relatively flat abyssal plains with no effective reflecting surfaces.

Bottom line: the SAN JUAN event is unique and should be analytically exploited by those with the required processing and display systems.

Re: Retrospective on the Loss of the ARA SAN JUAN (S-42)

Bruce, thanks for this very informative review. I'm wondering if any of this data you mentioned was used in the location of the lost sub during the extensive search operations.

Re: Retrospective on the Loss of the ARA SAN JUAN (S-42)

Stephen:

i leave it to Argentine authorities to answer your question.

Best,

Bruce

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