Astrophysicists build radio-telescopes the size of multiple football fields trying to pick up (and then sort out) radiation frequencies, particularly low frequency, of particular sources of energy they are trying to find.
How Neutrinos would be gathered and analyzed for very specific sources like submarines is beyond me
Neutering detection has been done in the past in deep salt mines with large containers full of carbon tetrachloride surrounded by sensitive scintillating (very sensitive) photo detectors. There have been semiconductor plastc-based photo detectors but I’ve never heard of any that can capture neutrons. Neutrinos just do react with much!