Comment by Animats

JDAMs apparently have had an inertial system for backup for some time. MEMS gyros are good enough to guide from release to target. DARPA has quietly been working on compact, low-cost guidance without GPS for a while.[1] Doesn't seem to have filtered down to the commercial market yet, and that's probably not an accident.

[1] https://www.darpa.mil/program/micro-technology-for-positioni...