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The following is the text of a letter set to the Director of Naval Nuclear Propulsion by R. Bruce Rule on July 3 of this year. It is his analysis on the probable cause of the loss of the USS Thresher (SSN 593) in April, 1963:
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3 July 2012
From: R. B. Rule, 3931 Brookfield Ave, Louisville, KY, 40207-2001
To: ADM K. H. Donald, Director, Naval Nuclear Propulsion, 1333 Issac Hull Ave. SE, Washington, DC 20376
Subj: Why the USS THRESHER (SSN-593) Was Lost
In April 1963, the originator, then the Analysis Officer at the Sound Surveillance System (SOSUS) Evaluation Center in Norfolk, VA, had just completed the U.S. Nuclear Submarine Acoustic Data Handbook, a comprehensive summary of the low frequency, narrowband acoustic signature characteristics of all U.S. nuclear submarines then operational, including the USS THRESHER (SSN-593). That document was based on analysis of more than 700 acoustic detection events of all nuclear submarines.
Acting in that capacity, and with those technical qualifications, the originator, subsequently the lead acoustic analyst at the Office of Naval Intelligence for 42 years and the author of the book reviewed on page 151 of the WINTER 2012 issue of THE SUBMARINE REVIEW (WI12TSR), called in acoustic data from all Atlantic SOSUS stations to determine if the loss of the USS THRESHER had been acoustically detected. That analysis identified a signal of extremely high amplitude produced by the collapse of the THRESHER pressure hull at 09:18:24R on 10 April 1963. The derived position - a four nautical mile (nm) by eight nm ellipse with a major axis oriented 040-220 - provided the basis for the successful search for the THRESHER wreckage.
That analysis also determined the THRESHER non-vital electrical bus, after two minutes of line-frequency instability, failed for unknown reasons at 0911R while the nuclear reactor coolant pumps (RCPs) were in FAST. (Note: the SSTGs were not acoustically detected; the instability of the non-vital bus was derived from measured instability in the RCP rotational-rates with determination of the non-vital bus line frequency by correcting for the 2.5 percent slip of the RCP drive motors; also note that the signal strength of the RCP sources at 0911R, at a detection range of about 30 nm, indicated that had the RCPs been shifted to SLOW at 0911R, they should still have been acoustically detected - but no such detection occurred.) The electrical load thrown on the vital bus at 0911R by the failure of the non-vital bus with the RCPs in FAST exceeded the capabilities of the vital bus; the RCPs (initially detected at 0845R in FAST as THRESHER, according to the deep-dive OP-PLAN, was approaching a depth of 1000 feet) went off-line and the reactor scrammed at 0911R. The coincident detection of an acoustic signature component at a fixed ratio relative to the RCP source unique to S5W RCPs confirmed the SOSUS detection was THRESHER. There were no acoustic detections by SOSUS of any THRESHER main propulsion sources as would have been probable had speeds above about 14 knots been employed. The author provided the above assessments of RCP operating mode and loss of signal in testimony before the THRESHER Court of Inquiry (COI) with supporting testimonies by BUSHIPS Code 345 and the David Taylor Naval Ships Research and Development Center personnel, respectively, a CAPT Leahy and Mr. Sam Savastin.
At 0913R, two minutes AFTER the reactor scrammed, THRESHER informed her escort ship, the USS SKYLARK (ASR-20), by underwater telephone, that she was (quote) experiencing minor difficulty.(end quote) The COI concluded the rupture of a silver-brazed, sea-connected pipe had produced flooding in the engine room that shorted-out electrical systems causing the scram, an assessment still accepted at the highest levels within the Navy; however, that assessment requires that flooding at test-depth that resulted in a reactor scram and a loss of propulsion capability be described by THRESHER as a (quote) minor difficulty. (end quote)
At 0917R, SKYLARK received a final communication from THRESHER that contained the number 900. That number is assessed to have been the depth in feet (referenced to test-depth as required by the deep-drive OP-PLAN security directive) by which THRESHER had exceeded her test-depth of 1300 feet, or 2200 feet. With an estimated average sink-rate of about 130 feet per minute (900 feet/7 mins), the THRESHER pressure-hull collapsed at 09:18:24R at a depth of about 2400 feet, more than 400 feet below her estimated collapse depth. Independent confirmation of that assessment has been provided by a post COI testimony analysis of the collapse event acoustic bubble-pulse signal frequency which indicated a depth between 2000 and 2400 feet. (See "Technical Comments" page 134 of the WI12TSR.) The originator has no information on the change in displacement produced by hull compression at great depth and the extent to which that decrease could have accelerated the THRESHER sink-rate.
There is not now - nor was there in 1963 - any evidence in the specific case of THRESHER to support the COI conclusion that the rupture of a silver-brazed, sea-connected pipe caused a reactor scram. THRESHER's 0913R transmission to SKYLARK - which make no mention of flooding - and analysis of the SOSUS acoustic data are consistent with failure of the non-vital electrical bus which resulted in a reactor scram at test-depth because the RCPs were operating in FAST. Unable to deballast because of a subsequently confirmed ice-formation condition in the high-pressure air lines, THRESHER sank to collapse at extreme depth without any prior flooding. Both the pressure hull and all sea-connected systems survived well beyond design specifications. To repeat, there was not - as maintained on page 122 of the WI12TSR - any (quote) failure of a silver-brazed fitting in the engine room, with immediate flooding, and subsequent emergency shutdown of the nuclear reactor (scram due to spray on the engine room affecting electrical control panels) (end quote); hence, it is wrongly asserted, also on page 122, that Portsmouth Naval Shipyard personnel were responsible for the loss of the USS THRESHER because of the failure of a silver-brazed fitting.
The bubble-pulse data indicates the THRESHER pressure hull and all internal compartments were completely destroyed in less than one-tenth of a second (100 milliseconds), significantly less than the minimum time required for human perception of any event: 50 milliseconds for retina integration plus 100 milliseconds for cognitive integration. Measurements made during the lowering and recovery of an instrumented diesel submarine to collapse depth are consistent with the conclusion that the water-ram produced by the initial breaching of the THRESHER pressure hull at 2400 feet traversed the diameter of the pressure hull in about 0.005 seconds (five milliseconds), a speed of about 4000 mph. That force would have torn the pressure hull longitudinally and vertically as verified by imagery of the THRESHER wreckage. Even allowing for differences in pressure hull design, the extent of the damage to THRESHER, compared to the USS SCORPION (SSN-589), which collapsed at 1530 feet, indicates THRESHER collapsed at significantly greater depth.
The above discussed information on the failure of the non-vital bus, the RCP operating mode and implications for a reactor scram are provided in COI documents available in the public domain.
As of March 2007, the Office of Naval Intelligence still held a photo-copy of the SOSUS paper display (LOFARgram) upon which the above assessments are based. There were no SOSUS recordings of the THRESHER event. The original SOSUS LOFARgram data from all Atlantic stations - except Barbados, which was bathymetricalty blocked - were destroyed by SOSUS Evaluation Center personnel when the data was more than five years old and because it was concluded another submarine would not be lost. The date of destruction of the original THRESHER acoustic data was 22 May 1968, the same day on which it was subsequently determined the USS SCORPION was lost.
With the approach of the 50th anniversary in 2013 of the loss of THRESHER, it would be appropriate for the Navy to officially acknowledge why the USS THRESHER was lost for the benefit of surviving family members and friends of those onboard who may find some solace in the knowledge that the collapse event occurred too fast to be apprehended by those onboard, and also for the benefit of those surviving Portsmouth Naval Shipyard personnel who continue to be falsely implicated in the loss of the USS THRESHER by assertions that a silver-brazed fitting failed.
As previously stated, the THRESHER pressure hull and all sea-connected systems significantly exceeded design specifications; there was no flooding before collapse of the pressure hull at extreme depth.
Bruce Rule
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Comments from those who served?
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3 July 2012
From: R. B. Rule, 3931 Brookfield Ave, Louisville, KY, 40207-2001
To: ADM K. H. Donald, Director, Naval Nuclear Propulsion, 1333 Issac Hull Ave. SE, Washington, DC 20376
Subj: Why the USS THRESHER (SSN-593) Was Lost
In April 1963, the originator, then the Analysis Officer at the Sound Surveillance System (SOSUS) Evaluation Center in Norfolk, VA, had just completed the U.S. Nuclear Submarine Acoustic Data Handbook, a comprehensive summary of the low frequency, narrowband acoustic signature characteristics of all U.S. nuclear submarines then operational, including the USS THRESHER (SSN-593). That document was based on analysis of more than 700 acoustic detection events of all nuclear submarines.
Acting in that capacity, and with those technical qualifications, the originator, subsequently the lead acoustic analyst at the Office of Naval Intelligence for 42 years and the author of the book reviewed on page 151 of the WINTER 2012 issue of THE SUBMARINE REVIEW (WI12TSR), called in acoustic data from all Atlantic SOSUS stations to determine if the loss of the USS THRESHER had been acoustically detected. That analysis identified a signal of extremely high amplitude produced by the collapse of the THRESHER pressure hull at 09:18:24R on 10 April 1963. The derived position - a four nautical mile (nm) by eight nm ellipse with a major axis oriented 040-220 - provided the basis for the successful search for the THRESHER wreckage.
That analysis also determined the THRESHER non-vital electrical bus, after two minutes of line-frequency instability, failed for unknown reasons at 0911R while the nuclear reactor coolant pumps (RCPs) were in FAST. (Note: the SSTGs were not acoustically detected; the instability of the non-vital bus was derived from measured instability in the RCP rotational-rates with determination of the non-vital bus line frequency by correcting for the 2.5 percent slip of the RCP drive motors; also note that the signal strength of the RCP sources at 0911R, at a detection range of about 30 nm, indicated that had the RCPs been shifted to SLOW at 0911R, they should still have been acoustically detected - but no such detection occurred.) The electrical load thrown on the vital bus at 0911R by the failure of the non-vital bus with the RCPs in FAST exceeded the capabilities of the vital bus; the RCPs (initially detected at 0845R in FAST as THRESHER, according to the deep-dive OP-PLAN, was approaching a depth of 1000 feet) went off-line and the reactor scrammed at 0911R. The coincident detection of an acoustic signature component at a fixed ratio relative to the RCP source unique to S5W RCPs confirmed the SOSUS detection was THRESHER. There were no acoustic detections by SOSUS of any THRESHER main propulsion sources as would have been probable had speeds above about 14 knots been employed. The author provided the above assessments of RCP operating mode and loss of signal in testimony before the THRESHER Court of Inquiry (COI) with supporting testimonies by BUSHIPS Code 345 and the David Taylor Naval Ships Research and Development Center personnel, respectively, a CAPT Leahy and Mr. Sam Savastin.
At 0913R, two minutes AFTER the reactor scrammed, THRESHER informed her escort ship, the USS SKYLARK (ASR-20), by underwater telephone, that she was (quote) experiencing minor difficulty.(end quote) The COI concluded the rupture of a silver-brazed, sea-connected pipe had produced flooding in the engine room that shorted-out electrical systems causing the scram, an assessment still accepted at the highest levels within the Navy; however, that assessment requires that flooding at test-depth that resulted in a reactor scram and a loss of propulsion capability be described by THRESHER as a (quote) minor difficulty. (end quote)
At 0917R, SKYLARK received a final communication from THRESHER that contained the number 900. That number is assessed to have been the depth in feet (referenced to test-depth as required by the deep-drive OP-PLAN security directive) by which THRESHER had exceeded her test-depth of 1300 feet, or 2200 feet. With an estimated average sink-rate of about 130 feet per minute (900 feet/7 mins), the THRESHER pressure-hull collapsed at 09:18:24R at a depth of about 2400 feet, more than 400 feet below her estimated collapse depth. Independent confirmation of that assessment has been provided by a post COI testimony analysis of the collapse event acoustic bubble-pulse signal frequency which indicated a depth between 2000 and 2400 feet. (See "Technical Comments" page 134 of the WI12TSR.) The originator has no information on the change in displacement produced by hull compression at great depth and the extent to which that decrease could have accelerated the THRESHER sink-rate.
There is not now - nor was there in 1963 - any evidence in the specific case of THRESHER to support the COI conclusion that the rupture of a silver-brazed, sea-connected pipe caused a reactor scram. THRESHER's 0913R transmission to SKYLARK - which make no mention of flooding - and analysis of the SOSUS acoustic data are consistent with failure of the non-vital electrical bus which resulted in a reactor scram at test-depth because the RCPs were operating in FAST. Unable to deballast because of a subsequently confirmed ice-formation condition in the high-pressure air lines, THRESHER sank to collapse at extreme depth without any prior flooding. Both the pressure hull and all sea-connected systems survived well beyond design specifications. To repeat, there was not - as maintained on page 122 of the WI12TSR - any (quote) failure of a silver-brazed fitting in the engine room, with immediate flooding, and subsequent emergency shutdown of the nuclear reactor (scram due to spray on the engine room affecting electrical control panels) (end quote); hence, it is wrongly asserted, also on page 122, that Portsmouth Naval Shipyard personnel were responsible for the loss of the USS THRESHER because of the failure of a silver-brazed fitting.
The bubble-pulse data indicates the THRESHER pressure hull and all internal compartments were completely destroyed in less than one-tenth of a second (100 milliseconds), significantly less than the minimum time required for human perception of any event: 50 milliseconds for retina integration plus 100 milliseconds for cognitive integration. Measurements made during the lowering and recovery of an instrumented diesel submarine to collapse depth are consistent with the conclusion that the water-ram produced by the initial breaching of the THRESHER pressure hull at 2400 feet traversed the diameter of the pressure hull in about 0.005 seconds (five milliseconds), a speed of about 4000 mph. That force would have torn the pressure hull longitudinally and vertically as verified by imagery of the THRESHER wreckage. Even allowing for differences in pressure hull design, the extent of the damage to THRESHER, compared to the USS SCORPION (SSN-589), which collapsed at 1530 feet, indicates THRESHER collapsed at significantly greater depth.
The above discussed information on the failure of the non-vital bus, the RCP operating mode and implications for a reactor scram are provided in COI documents available in the public domain.
As of March 2007, the Office of Naval Intelligence still held a photo-copy of the SOSUS paper display (LOFARgram) upon which the above assessments are based. There were no SOSUS recordings of the THRESHER event. The original SOSUS LOFARgram data from all Atlantic stations - except Barbados, which was bathymetricalty blocked - were destroyed by SOSUS Evaluation Center personnel when the data was more than five years old and because it was concluded another submarine would not be lost. The date of destruction of the original THRESHER acoustic data was 22 May 1968, the same day on which it was subsequently determined the USS SCORPION was lost.
With the approach of the 50th anniversary in 2013 of the loss of THRESHER, it would be appropriate for the Navy to officially acknowledge why the USS THRESHER was lost for the benefit of surviving family members and friends of those onboard who may find some solace in the knowledge that the collapse event occurred too fast to be apprehended by those onboard, and also for the benefit of those surviving Portsmouth Naval Shipyard personnel who continue to be falsely implicated in the loss of the USS THRESHER by assertions that a silver-brazed fitting failed.
As previously stated, the THRESHER pressure hull and all sea-connected systems significantly exceeded design specifications; there was no flooding before collapse of the pressure hull at extreme depth.
Bruce Rule
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Comments from those who served?
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