The two which I’ve read are concerning are using the ferromagnetic material in a sub to detect tiny variations in the magnetic field using supercooled sensors a

The two which I’ve read are concerning are using the ferromagnetic material in a sub to detect tiny variations in the magnetic field using supercooled sensors and just better computers and acoustic sensors to extract more signal from well below the noise floor. There’s also some more science fiction level technologies proposed like using the nuclear signature of a sub’s reactor or using space based LIDAR to detect signs of the wake of a submerged submarine but I’ll defer judgment on those for now. But longer term I wouldn’t completely count them out.