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Why the Argentine Submarine SAN JUAN Was Lost and Who Was Responsible

Request all further disseminate this assessment as quickly and as widely as possible.Link to electronic document follows separately ASAP.

The Argentine Submarine SAN JUAN
Was Lost Because of Crew Error.


Messages sent by the Argentine (ARA) submarine SAN JUAN (S-42) before submerging at 1152 Greenwich Mean Time (GMT) on 15 Nov 2017 confirmed that flooding of the forward battery compartment had caused electrical short-circuits, a condition which produces free hydrogen, an odorless, colorless, and highly-explosive gas. Unable to ventilate the submarine while submerged, the hydrogen slowly built to explosive levels.

Analyses of acoustic data collected by remote underwater sensors (hydrophones) confirm the hydrogen exploded at 1330 GMT, 98 minutes after the SAN JUAN submerged. The explosion – with an estimated power equal to 10 kg (22 lbs) of TNT - did not breach the pressure-hull but killed the entire SAN JUAN crew instantly: in 30 milliseconds (0.030s). The crew never knew the explosion occurred because the minimum time required for human perception of an event is 80-100 milliseconds. The pressure-pulse produced by the hydrogen explosion propagated throughout the SAN JUAN at a speed of about 1400 m/s (3130 statute miles per hour). The pressure of that pulse is estimated to have been between 10 and 14 bars (150-200 psi), several time the level 100-percent fatal to humans.

With the crew dead, and propulsion lost because of internal damage, the SAN JUAN sank from a known operating depth of 40m (130ft) to collapse (implode) in 35 milliseconds at 1351 GMT on 15 Nov 2017 at a depth of 468m (1536ft) where the water-pressure was 46 bars (676psi) . The elapsed time between acoustic detections of the hydrogen explosion and collapse was 1234 seconds (s). The derived average SAN JUAN sink-rate was 38cm/s (1.15ft/s) (69f/m) or 0.68 knots.

This compares to an average sink-rate of 0.36cm/s (1.12ft/s) (67f/m) (0.66 knots) for the US nuclear submarine SCORPION (SSN 589) which experienced two battery-generated hydrogen explosions within 0.2s at 18:20:44 GMT on 22 May 1968 while at a depth of about 18m (60ft). SCORPION then sank over the following 1310s to collapse in 37 milliseconds at 18:42:34 GMT at a depth of 466m (1530ft). The sequence of events responsible for these hydrogen explosions cannot be determined from available information.

Based on analysis of images of the SCORPION wreckage, the SCORPION Analysis Group determined in 1970 that the observed destruction of the area above the battery well had been caused by “a violent force moving fore to aft and low in the battery well.” (Argentine authorities have 67,000 images of the SAN JUAN wreckage taken by Ocean Infinity autonomous underwater vehicles.)

Analysis confirmed the energy level of the SAN JUAN collapse event acoustic signal was equal to the explosion of 5216 kg (11,475 lbs) of TNT. The duration of the collapse was 35 milliseconds (0.035s). The collapse signal was acoustically detected at a distance of 7715 km (5,567 statute miles) with an energy level sufficient to have been detected at distances greater than the 40,000 km (24,900 statute mile) circumference of the earth if an unobstructed deep-water transmission path had existed.

Analysis of acoustic detections of the near-field echo-pattern of the SAN JUAN collapse (implosion) signal confirmed the event occurred above the northern-facing wall of an undersea canyon oriented WNW to ESE, and that the wreck of the SAN JUAN would be found strewn down that canyon wall which is exactly where it was found on 16 November 2018 - in multiple major sections - at depths between 920m and 945m (3020ft and 3100ft)

Analysis of acoustic data also confirmed a small structure – possibly a spherical tank – had survived the collapse (implosion) of the SAN JUAN pressure-hull intact. That small structure did not collapse until 20 minutes after the wreckage impacted the canyon wall. The sink-rate of the SAN JUAN wreckage is estimated to have been about 5.5ms (11 knots) with bottom impact occurring about 1.5 minutes after collapse or at about 1353 GMT on 15 November 2017. The bottom impact was not acoustically detected nor was such a detection expected. Bottom impacts are normally not detected at distances greater than five times water-depth at the impact site.


The USS SCORPION's six torpedo tubes survived the implosion of the pressure-hull to collapse at depths between 1030m (3370ft) and 1390m (4570ft). The collapse of 12 additional smaller structures within the sinking wreckage were acoustically detected. The first of these 12 events occurred when the depth of the wreckage was about 620m (2035ft); the second when the depth of the wreckage was about 970m (3180ft): the last when the depth of the wreckage was about 1570m (5150ft). The depth of the SCORPION wreck-site is 3370m (11,100ft)
This information suggests the SAN JUAN wreckage at depths as great as 945m (3100ft) may contain small structures already stressed near collapse. If efforts are made to recover the SAN JUAN wreckage, forces applied by those activities could trigger implosions that would further damage both the wreckage and the recovery system. Currently, there is no apparent justification for disturbing the SAN JUAN grave-site - which is potentially a mine-field - to address questions that already have been definitively answered: (1) why the SAN JUAN was lost, and (2) who was directly and immediately responsible for the disaster.

Also note that the Soviet Project 629A SSB K-129 (NATO: GOLF II) was lost on 11 March 1968 because hydrogen explosions contained within in the pressure-hull occurred at 1158:58, 11:59:43 and 11:59:47, all times GMT. The first compartment (torpedo room) of the K-129 recovered on 4 August 1974 by the Central Intelligence Agency salvage ship, the HUGHES GLOMAR EXPLORER, showed extensive damage from a high temperature, high velocity compressive event. Images of the K-129 wreckage showed extreme damage to the forward end of the after battery compartment. This information provides a basis for assessing conditions that may exist within the SAN JUAN wreckage if those conditions have not already been established by analyses of imagery of the SAN JUAN wreckage. The sequence of events responsible for the hydrogen explosions that occurred within the K-129 pressure-hull cannot be determined from available information.


Collectively, the SAN JUAN messages and analyses of acoustic signals confirm the disaster had a single cause: the decision by the crew to submerge which allowed the battery-generated hydrogen to reach explosive levels.

Had the SAN JUAN remained on the surface fully ventilating all compartments, the disaster would not have occurred. There is no evidential basis to support an assessment that ARA personnel who were ashore when the SAN JUAN was lost bore any responsibility for the disaster. To contend that those ashore were complicit in the loss of the SAN JUAN is like asserting that airport personnel who authorize the departure of a plane would be responsible if that plane crashed hours later because of pilot error.


The writer is profoundly grateful to citizens/residents of Argentina, Germany, Norway, Spain, Uruguay, and eight US states for their contributions to the derivation and dissemination of earlier versions of this final assessment of why the ARA SAN JUAN was lost. No individual or military or civilian organization working alone could have achieved this definitive result which is based entirely on information derived from unclassified sources.


As the Analysis Officer at the US Navy's Sound Surveillance System Data Evaluation Center, Bruce Rule testified before the Navy's THRESHER Court of Inquiry on 18 April 1963 and subsequently was the lead acoustic analyst at the US Office of Naval Intelligence for 42 years. He has written books (technical assessments) on the losses of the US nuclear submarines THRESHER and SCORPION, royalties declined.