The U.S. Coast Guard said Thursday a remote operated vehicle (ROV) discovered a "debris field" near the Titanic wreckage site where a submersible went missing.
According to submariners in other communities, the worst part would be any period of time where they knew they were sinking. That could be an hour of slowly falling from periscope depth or no time at all if the hull failed at a deep enough depth. The water forms a piston much like one in a truck engine that compresses the air enough to cause combustion. Any of the three things in that nano second will kill you before your body can process the information. The water hammer, the pressure shift, and the implosion all occur too quickly for the nerves to transmit the information.
A Navy official says "an acoustic anomaly consistent with an implosion" was detected shortly after the Titan lost contact with the surface. This official said the information was relayed to the Coast Guard team which used it to narrow the radius of the search area.
I guess they wanted to keep going until there was undeniable evidence of their peril. An "acoustic anomaly" alone isnt really enough to say "they were pancaked let's go home"