[Moonman62]

Inertial navigation was used long before GPS.

https://en.wikipedia.org/wiki/Inertial_navigation_system

[pingman]

Anchor Crankers rejoice!

[Ace's Dad]

Inertial navigation was used long before GPS

Inertial navigation was used successfully long before GPS.

Inertial was compact enough, and accurate enough for Navy aircraft, such as the P-3 Orion, many years ago.

[phormer phrog phlyer]

Beat me to it, sounds like a version of inertial.

It still has to know where it is at the start.

I flew 747-4, they used multiple GPS and Inertial systems, that worked together.