Canuckabroad:

The current scenario proposed was that there was catastrophic failure at the time when the vessel stopped sending communications, between 1:45 and 2:00 into the mission.  At that depth there wouldn't have been any suffering.  It is a small but significant mercy that they probably weren't aware of what was happening.

My best guess is that the reason sonar buoys are required for precision is because there are limits to how effectively you can pick up some sounds from almost 4km below the surface - having additional sensors and having a wider range for signals to arrive make it more likely to be noticed - just like how larger telescopes (including telescopes with multiple arrays) work better than smaller ones.

Looks like the US Navy SOSUS network heard the implosion days ago , 

"An implosion was heard near the site where debris was located on Thursday, about 500m from the Titanic shipwreck, soon after the sub disappeared, according to the report.

The system is used to monitor enemy submarines, and the Navy asked that it not be identified due to national security concerns, the Journal reported.

https://www.independent.co.uk/news/world/americas/titan-submarine-implosion-navy-debris-microphones-b2362685.html

Interesting question.  If there had been this evidence of a likely implosion days ago, would we have seen the same urgent international deployment of resources by those hoping to rescue survivors (with the related costs which are now being mentioned)?  Clearly nobody here is in a position to decide what is appropriate for military to reveal regarding their sonar capability - but the way it's presented here as "Oh yeah, we heard about that days ago but didn't think it was appropriate to tell you then (but it's now fine?)" isn't ideal.

"A U.S. Navy acoustic system detected an ‘anomaly’ Sunday that was likely the Titan’s fatal implosion, according to a senior military official.

 

The Navy went back and analysed its acoustic data after the Titan submersible was reported missing Sunday. Coast Guard officials on Thursday announced that the craft suffered a catastrophic implosion, killing all five aboard.

 

That anomaly was “consistent with an implosion or explosion in the general vicinity of where the TITAN submersible was operating when communications were lost,” according to the senior Navy official.

 

The official spoke on condition of anonymity to discuss a sensitive acoustic detection system.

 

The Navy passed on the information to the Coast Guard, which continued its search.

 

AP

The surveillance network is not designed to look for things imploding, its listening for the cavitation of Submarines,  plus it will be heavily automated, the days of having sonar operators with headsets on listening live is likely long gone...

My read is that once it went missing the navy went back and listened to the data from when it entered the water, they heard something that could be an implosion,  and told the Coast Guard, 

The Coast Guard had other information ( the apparent banging at 30 minutes intervals)  and weighed up to continue to search, 

Maybe they had decided  they were looking for wreckage, may be  not, but I guess they concluded that it was likely best to continue to search no matter whet they found..

the thing with information like that is it has to be analysed, determined if its what you need, then it needs to be declassified, which would again involve being analysed, but then also to determine if releasing that information would give away any information about the capibilities of the system it was recorded on.

Its not a simple process.

Bung: 
The US Coast Guard mentioned that it would have occurred before their sonar buoys were deployed or else the implosion would have been detected. Why didn't the sonar equipment on the Oceangate ship hear it?

What sonar equipment is on the oceangate ship? if the implosion was outside the frequency range of the sonar set, wasnt being listened to, wasnt recorded, any manner of different things.

Canuckabroad:

Interesting question.  If there had been this evidence of a likely implosion days ago, would we have seen the same urgent international deployment of resources by those hoping to rescue survivors (with the related costs which are now being mentioned)?

“The U.S. Navy conducted an analysis of acoustic data and detected an anomaly consistent with an implosion or explosion in the general vicinity of where the Titan submersible was operating when communications were lost,”

Bung: "But US government bureaucracy has hampered rescue efforts as essential equipment remains stuck on the island of Jersey, while the required paperwork is signed for it to be imported."

Handsomedan:

There's a few bits and pieces that have been reported to be not fit for purpose, too...

* Minimum operating life 90 days

 

* Detectable in deep sea down to more than 20,000ft (6,096m)

 

* Detection range up to 16nm (29km) which is based on a depth of 3,500m

wellygary:

 

Looks like the US Navy SOSUS network heard the implosion days ago , 

 

"An implosion was heard near the site where debris was located on Thursday, about 500m from the Titanic shipwreck, soon after the sub disappeared, according to the report.

 

The system is used to monitor enemy submarines, and the Navy asked that it not be identified due to national security concerns, the Journal reported.

 

https://www.independent.co.uk/news/world/americas/titan-submarine-implosion-navy-debris-microphones-b2362685.html

 

 

 

looks like the cat's out of the bag!