Tomahawk cruise missiles originally used terrain following. (1983) Now they have GPS capability but I think terrain following is still an option.

It’s insane to me they had stuff like terrain following working in the early 80’s

A fairly in-depth explanation of one part of the system from a 1994 paper: https://secwww.jhuapl.edu/techdigest/Content/techdigest/pdf/...

Or at least something slightly lower tech like an electronic compass that will keep a back bearing and fly the reverse course if signal is lost.

But it has to be a question of cost too. Drones are attritable by their nature and there may be no more reason to try to recover one than you would recover a discharged bullet.

Usually for tactical drones they get fitted with an IMU (Inertial measurement unit / gyros) for when GPS signal is lost. That way the drone can continue operation but do suffer from drift the longer the GPS signal is not available. But cheap IMU's fitted on smaller drones has very poor accuracy / drift.

A bigger upset is loss of communications, very few if any drones operate autonomously currently, and if there is loss of communications they may try to return to base. Off course it is more difficult to jam line of sight or drone to satellite communications than GPS.

> if there is loss of communications they may try to return to base.

I wonder if either or both sides are patching this out of software - otherwise, communications jamming becomes a quick way to make the drone lead the enemy straight to your base.