Even Submarines have to use their sonar at some point just to see what is around them and correct for minor drift in course. Most of the time they use passive sonar (i.e. listening to the ambient noise) to avoid revealing their location, but even with gyroscopic inertial navigation assistance, tiny errors accumulate over time, and they have to send out a sonar pulse to see what is around them in the water.
They also periodically surface to attain a gps signal and receive comms, since it's pretty hard to penetrate 1000 feet of water with a radio signal.
Even Submarines have to use their sonar at some point just to see what is around them and correct for minor drift in course. Most of the time they use passive sonar (i.e. listening to the ambient noise) to avoid revealing their location, but even with gyroscopic inertial navigation assistance, tiny errors accumulate over time, and they have to send out a sonar pulse to see what is around them in the water.
They also periodically surface to attain a gps signal and receive comms, since it's pretty hard to penetrate 1000 feet of water with a radio signal.