A2/AD.

 This is coolbert:

More on the "big data" approach to submarine detection:

 "Are Submarines About to Become Obsolete?"

"methods mature that rely on phenomena other than sounds emanating from a submarine. These techniques include lower frequency active sonar and non-acoustic methods that detect submarine wakes or (at short ranges) bounce laser or light-emitting diode (LED) light off a submarine hull. The physics behind most of these alternative techniques has been known for decades, but was not exploited because computer processors were too slow to run the detailed models needed to see small changes in the environment caused by a quiet submarine. Today, 'big data' processing enables advanced navies to run sophisticated oceanographic models in real time to exploit these detection techniques."

Submarines becoming obsolete in the conventional sense of the word submarine as we understand it. A MANNED submarine  of the conventional sort, nuclear or diesel/electric powered.

The use of drones [UUV] is the answer? Expendable and much cheaper not totally undetectable but much more so and UNMANNED, the loss not so significant?

coolbert.