Very classified so we only know bits and pieces. "Inertial navigation" is part of it - basically very precise dead reckoning. Using specialist equipment like laser ring gyros to get precise measurements.
Then also some other equipment like a magnetometer and magnetographic maps of the world to provide references to counteract the drift in any inertial navigation.
Again, this is what we know about the state of the art 20 years ago:
For receiving (very very slowly) there is VLF, as the other comments have said. Can be done underwater. Think 160 character tweets that take minutes to arrive.
One option is to release a buoy that floats to the surface, waits a while and then transmits the payload. This allows the submarine to be out of the area when the transmission happens. This gets you "don't know where the sub is" but doesn't necessarily get you "didn't know there was even a sub there".
Alternatively, the submarine can come to periscope depth - so underwater but able to raise an antenna above the surface (or maybe close to it). Then something sophisticated like direct laser communication to a satellite can happen, allowing for high data rate bidirectional comms. Assuming you aren't detected by coming up, then this SHOULD allow for completely undetectable comms.
They can trail an antenna behind the boat underwater that receives low frequency radio waves carrying short signals that basically tell them to come up to a higher depth to receive a longer message.
Communicating from buoy to an underwater sub is hard (ULF antennas are 100s of metres long) and more importantly would give away there was a vessel there somewhere.
Also that would only locate where the buoy is, not the sub and the sub probably needs more precise location than that. They want to be able to manoeuvre around underwater terrain features and things.
Comments
How does a modern submarine navigates today?
Very classified so we only know bits and pieces. "Inertial navigation" is part of it - basically very precise dead reckoning. Using specialist equipment like laser ring gyros to get precise measurements.
Then also some other equipment like a magnetometer and magnetographic maps of the world to provide references to counteract the drift in any inertial navigation.
Thank you for the information - and what about communication? I don't think they have an antenna that reaches out to the surface?
Again, this is what we know about the state of the art 20 years ago:
For receiving (very very slowly) there is VLF, as the other comments have said. Can be done underwater. Think 160 character tweets that take minutes to arrive.
One option is to release a buoy that floats to the surface, waits a while and then transmits the payload. This allows the submarine to be out of the area when the transmission happens. This gets you "don't know where the sub is" but doesn't necessarily get you "didn't know there was even a sub there".
Alternatively, the submarine can come to periscope depth - so underwater but able to raise an antenna above the surface (or maybe close to it). Then something sophisticated like direct laser communication to a satellite can happen, allowing for high data rate bidirectional comms. Assuming you aren't detected by coming up, then this SHOULD allow for completely undetectable comms.
Very low frequency radio: https://en.wikipedia.org/wiki/Communication_with_submarines
They can trail an antenna behind the boat underwater that receives low frequency radio waves carrying short signals that basically tell them to come up to a higher depth to receive a longer message.
Can't they just release a buoy with a gps in it? That sounds overcomplicated
Lots of issues with that:
Communicating from buoy to an underwater sub is hard (ULF antennas are 100s of metres long) and more importantly would give away there was a vessel there somewhere.
Also that would only locate where the buoy is, not the sub and the sub probably needs more precise location than that. They want to be able to manoeuvre around underwater terrain features and things.