HalcyonDaze
Contributor
Ballard's been pretty open for a while now that the USN funded his Titanic search (and the manned dives the following year) with the stipulation that he first take his new toys and check out the wrecks of USS Thresher and USS Scorpion, both of which had already been located and photographed shortly after their losses (1963 and 1968, respectively). I don't think that was publicly acknowledged until at least a decade later (in addition to both subs being nuclear-powered, Scorpion had been on an operational patrol and sank with two Mark 45 ASTOR nuclear-tipped torpedoes onboard; not necessarily something to advertise). The only known Soviet sub loss in that general area of the Atlantic was K-219 down closer to Bermuda, and she didn't sink until October 1986, after Ballard made his first two trips to Titanic.Robert Ballard worked for the the CIA or a similar agency. His search for the Titanic was actually a cover story for looking for something else (I think it was a lost Russian sub, I am not solid any of this, going totally by memory). He almost certainly has better access into what information is available than most.
My guess is pretty much every modern navy in the Atlantic heard the bang. I bet the last few days have just window dressing on trying to avoid letting the Russians and the Chinese know exactly how thorough US/NATO monitoring of the Atlantic is. Everyone who is anyone in deep submersibles was probably very aware of what was going on.
I know composite materials are not great for pressure vessels. Fiber glass tanks have a finite life, unlike steel. When a fiber breaks it stays broken. Once they noticed the hull starting to fail, it was a runaway train. they just were not going up faster than hull was cracking. This is just my thoughts on the matter.
As far as SOSUS, they picked up something that matched an implosion, but I doubt it was an "everybody in the Atlantic heard it" deal or definitive enough for anyone to say "welp, they're done for, let's not even bother." If nothing else, until the wreckage was found the USN would have been raked over the coals for not putting in maximum effort (EDIT: an ex-USN congressional representative who should know better has already accused them of this); hell, 60 years later some idiots on the internet still believe Aaron Amick's BS about Thresher still hanging on a day after sinking (which like the "banging" noises heard looking for Titan, shows how tricky it is trying to interpret faint sounds in a complex environment while under stress).
I doubt it would be a huge secret that SOSUS heard it; that's been a known thing since the Cold War and one of the reasons the Soviets/Russians developed a number of "oceanographic research" nuclear submarines was to mess with that and other underwater infrastructure.