[dw1]

I am certainly not up on the state of the art, but I believe many of the principles are the same as I learned them years ago: detection using sound (very often from airborne sources via air-dropped sonabouys and dipping sonar, deployed to various depths) and magnetic anomaly detection (MAD).

Interestingly, one exercise I remember is evaluating passive sonar signals by what was being "masked", i.e. the intermittent absence of sounds as if something was blocking a source.

It is also interesting to note the "camouflage" systems developed at that time - the Prairie-Masker for example - a system that made it more difficult for the subs to determine surface ship identity and movement.

As said in a post above, there are many good books on modern ASW. My training was on the SQS-26 and I know the signal processing and system integration got a lot better since then - like with the SQS-53.

- USN STG3 (about a million years ago)