Thread by @BrynnTannehill

I've stayed quiet on the whole lost submarine thing since the beginning, because I am not an expert on underwater search and rescue. However, now that there's stuff about underwater acoustics, this is a bit more in my wheelhouse. 1/n

For background, I was qualified on the the BQQ-5G sonar system, and spent time underway as a sonar operator with the USS Augusta (SSN-710). I was also a pilot of SH-60B and P-3C sub-hunting aircraft. 2/n

The underwater environment is surprisingly noisy. Anything you hear isn't really proof of detection until you get some sort of secondary confirmation (going from possible submarine (POSS SUB) to CERT SUB). 3/n

Just because you see a line indicating a noise consistent with something, doesn't meant that's what it is. When you hear something, without confirmation generally all you can say is "noises consistent with X". Geologic noises can sound like explosions. 4/n

There's also the issue that sound waves curve underwater based on changes in temperature, pressure, and salinity. Judging distance and depth with hydrophones with passive detection is difficult. Distance requires cross-fixes. 5/n

I'm linking a sound file here that records the explosion of a Mk 24 homing torpedo, and the implosion of the submarine I-52 during WWII. Keep in mind, the sonoubuoys recording this were a likely less than 1000 yards from where this happened. 6/n maritime.org/sound/sonobuoy…

(If you're super interested, here's a video on the engagement. In a lot of ways, the basics of sub-hunting with sonobuoys still has a lot in common with how it was done in WWII). But, the take away is just how noisy it is. 7/n

During the Cold War, the US and NATO laid long lines of hydrophones over many parts of the North Atlantic to detect noises made by Soviet subs. This was called SOSUS. It was a top secret project at inception in the 1950s. The mission was declassified in 1991. 8/n

SOSUS continues to be used today. It is likely what detected the noises made by the implosion of the Titan. However, it is possible a SURTASS ship could have picked it up. 9/n en.wikipedia.org/wiki/SOSUS

Some hydrophones can tell what direction a sound came from, allowing a calculation of a cross-fix between multiple sensors. Given the distances involved, how there's always error, and the vagaries of sound propagation, you get a rough area where sound may have come from 10/n

So, what likely happened, is after Titan went missing, there was a review of SOSUS data. They found a noise consistent with implosion, in the area of where Titan was operating, at the time Titan was operating.

However, this was probably not definitive. 11/n

Until you find the wreckage, you cannot rule out tectonic activity, other military activity that was unknown to the US, potential commercial operations, etc... Yes, they likely knew that there was a low probability they were alive. 12/n

Long range passive sonar isn't proof. As long as there was a chance, they still had to make the attempt in case one of the other explanations for the noise was true. Given how small Titan was, the carbon fiber, and the depth involved, the noise was probably sharp and short. 13/n

There may have been detection of the bubbles going to the surface, and MAYBE the wreckage hitting the sea floor (the Pisces III hit the bottom going 40 mph). 14/n thedrive.com/the-war-zone/r…

But, this is a very long-winded explanation of why I reject the criticisms of the USG, USN, USCG, RCN, and RCCG for continuing the search despite knowing the crew had probably died. Passive sonar is maddeningly vague at times. There was still a chance. 15/n

I have great respect for the USCG and its unofficial ethos of ""You have to go out, but you don't have to come back!" I'll leave the discussion of rescuing rich people doing exceptionally dangerous things in home-made craft for another day.

But, the USCG did their job. 16/n

The capabilities and locations of current SOSUS arrays remain classified, which would explain much of the lack of transparency. You can reverse engineer knowledge of capabilities from detections

Chapter 3 of this doc is an underwater acoustics 101 17/n files.eric.ed.gov/fulltext/ED129…

Final note: I made a quick illustration of how acoustic lines of bearing create a search area based on known limitations in accuracy, and how this area can be very big if the noise is far away. This is also how you use multiple lines of bearing to get a fix. Forgive my PPT 18/n

Think of it as a risk calculation:

What's worse for the USG: searching for people who are probably already dead, and finding out they are, or calling off the search and finding out they were (past tense) still alive when the search was called off? The latter would be brutal 19/n