Communicating with submarines is actually a nightmare. The saltwater ruins most radio communications, so you have no chance to receive GPS signals, which are pretty weak even on the surface.
One thing the military does/did to communicate with subs is use low-bandwidth text-only very low frequency radio, but you need colossal transmitters and there's no way the mother ship carries one. Hydrophones are also an option, and IIRC NATO even has a working sound-based modem to transmit digital signals to subs, but not sure if that has spread in the civilian market.
One thing the military does/did to communicate with subs is use low-bandwidth text-only very low frequency radio, but you need colossal transmitters and there's no way the mother ship carries one. Hydrophones are also an option, and IIRC NATO even has a working sound-based modem to transmit digital signals to subs, but not sure if that has spread in the civilian market.