One of the few communications (by underwater telephone) from Thresher to the accompanying Submarine Rescue Vessel (ASR), during her fatal deep dive, was “experiencing minor difficulties, attempting to blow”, thought to be transmitted by the Thresher’s commanding officer.
In addition to this evidence of a problem, the SOSUS recordings during Thresher’s deep dive showed a pattern of intermittent noise that suggested interruptions of air flow.
Based on this information (and perhaps other factors), the Court of Inquiry asked Tinosa to conduct tests of its main ballast tank (MBT) blow system.
Thresher was the first submarine to have 4500 psi air banks (cylin ders located in the MBTs).
The previous maximum was 3000 psi and prior submarines had 3000 psi air systems running throughout the ship, without a need for reducing valves.
All of Thresher’s (and Tinosa’s) air systems were also 3000 psi; but two large 4500/3000 psi reducers served the 3000 psi systems from the 4500 psi storage cylinders. Thus, the 3000psi air used to blow the MBTs when surfacing went through these 4500/3000 psi reducers.
When Tinosa was preparing to fully test the MBT blow system alongside a pier (Tinosa was not yet ready for sea, but the air systems had been completed), a team of Shipyard engineers was assigned to help us with instrumentation, recording, etc. Through this team, the Shipyard expressed concern that a full pressure blow of MBTs alongside a pier (rather than submerged) might bulge or even rupture the MBTs.
For this reason, Tinosa’s first test of the MBT blow system was done with only 500 psi in the 4500 psi air banks; and instrumentation was placed on a MBT vent cover, topside on the ship, one forward and one aft.
[Note that this concern by the Shipyard is compelling evidence that a full test of the MBT blow system was not scheduled or conducted on Thresher before she went to sea. And, in fact, no such test was scheduled or planned for Tinosa at that point in time.]When the test was conducted on Tinosa with 500 psi in the air banks, there was essentially no measurable back pressure in the MBTs during the test.
The test was once again conducted with 1000 psi in the air banks, and once again the back pressure in the MBTs was nominal; about 1 psi as I recall.
Tinosa was then authorized by the Shipyard to do the full pressure test requested by the Court of Inquiry; and we charged all air banks to 4500 psi. With the air systems instrumented, including timers, we then conducted the full blow test simulating what a submarine would do at sea m an emergency.
When the MBT blow valves were opened on order there was a huge rush of air noise in the control room, then silence after a few seconds. Than a few seconds later another brief rush, then silence again. This pat tern was repeated over about a six-minute period until the blow valves were closed and the test terminated.
Air pressure in the air banks had only dropped a few hundred pounds; to about 4100 psi as I recal I.
We were shocked. The engineers and Tinosa personnel expected the air banks to be depleted in two or three minutes. We had witnessed less than one-tenth of the simulated deballasting (removal of sea water from the MBTs) that we expected.
An auxiliaryman who was stationed in the space where the two 4500/3000 psi reducers were located quickly reported that the reducers and upstream piping were covered in ice. The cause of the icing and reduced air flow was soon found — a strainer installed upstream of each reducer had collapsed, effectively blocking over 90% of the expected air flow.
No Tinosa crew members, officer or enlisted, were aware that the strainers were installed — nor were any of the Shipyard personnel in volved in the testing.
We were subsequently advised by the Shipyard that the strainers were installed at the request of the Marotta Valve Company because construction debris was interfering with the ability of the reducers to completely shut off air flow, thus tending to over-pressurize the 3000 psi air system. The strainers were supposed to be removed before the ships went to sea.
The strainers were conically shaped (before collapsing), pointed into the airstream, and were backed by a thick brass or bronze orifice with a small center hole (about ¼ inch diameter). The purpose of the orifice was to reduce the pressure differential across the strainer, so it would not collapse.
This worked during extensive routine use of the 3000 psi air system on Tinosa and during the MBT blow tests with 500 psi and 1000 psi in the air banks. But when the full pressure MBT blow test was conducted the strainers collapsed.
Thus, this observer’s impression is that the strainers on Thresher may have collapsed when an emergency blow of MBTs was commenced or may have been already collapsed or partially collapsed as the col lapsed strainers would pass enough air for routine 3000 psi air service and for a brief burst of air when surfacing from periscope depth when the Low Pressure Blower was the primary means of deballasting. So, it is quite possible that Thresher had been operating with collapsed or partially collapsed strainers for some time.
There was abundant evidence that the strainers were installed on Thresher, including:
- SOSUS patterns that showed the intermittent bursts of air noise as ice formed in the collapsed strainer and then blew out, then reformed, etc.; closely matching the pattern seen during tests on Tinosa.
- Testimony by Shipyard personnel to the Court oflnquiry that the strainers were installed on the
- Thresher Captain Wes Harvey’s statement “attempting to blow” on the underwater telephone
- The presence of the strainers on Tinosa
In assessing the impact of the degraded MBT blow system on Thresher’s attempts to reach the surface, it is important to understand the role of the propulsion system. Normally, a “Full Bell” (quickly re sulting in high speed of the ships propeller) would result in a rapid drive toward the surface. The data available strongly suggests that the reactor scrammed early during Thresher’s plight, and high levels of thrust from the propeller were not available. Subsequent to the loss of Thresher, Tinosa conducted tests (as did other ships) showing that use of decay heat from the reactor could provide a moderate level of propulsion for a few minutes after a scram – enough propulsion to be an important asset in an emergency such as Thresher experienced. But this capability was not available to Thresher. Naval Reactor’s procedures did not permit use of decay heat at the time. (Soon after the Thresher loss, the procedures were changed.)
Indeed, on Tinosa, and I expect on Thresher, the scram procedure required the upper level engine room watch to trip the main turbine inlet valves locally— to be re-set only after a full recovery from the scram, at least 20 or 30 minutes later. The Captain of Thresher most likely did not have the option of overriding procedures and using propulsion anyway.
Thus, the Main Ballast Tank blow system was the only means of bringing the ship to the surface, and the evidence is strong that it was seriously degraded. When one inspects the enclosed strainer, disabled may seem more accurate than degraded.
NOTES:
- During the tests of Tinosa’s MBT blow system, the question arose as to whether the results of a full blow test on the surface at dock side would closely simulate a full blow at or near test The ship yard (and BUSHIPS at the time) determined that flow to the main ballast tanks would be limited by “sonic choking” in the relatively small 3000 psi air lines to the MBTs; not by back pressure in the MBTs.
- Three colleagues, who were shipmates on Tinosa during the pe riod under discussion, reviewed this letter and the above observations and assisted in the quest for accuracy. These were:
- Clarence (Ed) Moore, CAPT. USN retired. Ed was Chief En gineer on Tinosa
- William (Bill) Smith, ADM. USN retired. Bill was Electrical and Reactor Control Officer on Tinosa
- Walter (Walt) Coakley, CAPT. USN retired. Walt was Weap ons Officer and an Engineering Officer of the Watch on Tinosa
