The best way to maintain communication with a submersible is a tether. The best way to know the position of a submersible is a tether. The best way to raise a submersible in trouble is a tether… this company chose to go another way. And, let’s be clear, even if they knew precisely where it was the odds are very good that they couldn’t possibly effect a rescue.
The grim truth is that everyone aboard is already dead, the hope is that it was a sudden implosion rather than slowly freezing, drowning, or asphyxiating.
And yeah, they knew pretty quick that a sound consistent with an implosion was heard at a time consistent with the loss of communication… not entirely sure why there wasn’t more communication of that earlier, though. Probably some fairly rich constituents pushing on the political side for a showy (and costly) rescue attempt that was always going to end up being a salvage and recovery operation.
Now that the engineering choices have become clear it’s no wonder this happened… they really had “disrupted” their way into a time bomb.
They are looking for this submersible by sonar. You don't need a nuclear submarine for sonar as it can done with ships ,sonobuoys dropped by aircraft or RV subs with sonar.