Perhaps those who know can comment on the current realities being faced with the recovery teams.
I am familiar with this field in the last 10 years or so. (LF, MF and HF) The capabilities of current gear are unbelievable. I have a "good ear"for CW (morse code) under very noisy conditions. When you use a "quite simple" DSP software in your computer audio adapter you can
see clearly signals impossible,
repeat, impossible to hear. Remember noise is inherently random but the ULB signal source is coherent. Fascinating field! But the recovery teams are in a different environment...