I admit that I don’t know much about submarine communications. But I’ve decide that the most analog possible approach for transmitting data to the surface would be Morse Code Bubbles.
Little vents on the top of the sub would open and close to release bubbles in a pattern of Morse Code that could be monitored at the surface. The vents could even be human-controlled. Very analog indeed.
– — .-. … . / -.-. — -.. . / -… ..- -… -… .-.…..