[jamesralph8555]

Its not the pressure, but the fact water blocks radio waves. Submarines can’t get GPS signals or transmit their location. Submarines have to rely on other means such as IMUs to track their own location.

[yayitswei]

What about a signal flare that floats to the surface?

[Mandatum]

I believe at a certain depth some things compress, density increases, buoyancy becomes negative - and they sink.