That does seem to be the theory.
Of course if we really are detecting these subs by some yet unknown, more or less, method, but which we don't want to expose, for obvious reasons, we still have plenty of ways to sink 'em, if and when the time comes. Why show our hand now?
For example, I seem to remember reading something about using radar or other sensors on satellites to detect the disturbance, (displacement of the water by the sub) caused by a moving sub.
I remember reading something 20 years ago about using lasers to detect the vibration of glass windows to determine the conversation going on within a room. My physics background saws that it would not be impossible (though difficult) to determine via some detectable wavelength such a disturbance as you note.
That’s a lot to hope. I hope our navy doesn’t get stuck on the wrong side of a paradigm shift, like the British in early 1942.