Especially cruise missiles and drones for which weight, power and size (and cooling) are not considerations.
Cruise missiles originally used terrain mapping, drones are more of less the same. You can supplement terrain mapping with inertial navigation using conventional accelerometers, and I am sure that they already do.
If you need an accelerometer to navigate a train, you’re on the wrong track, Casey Jones.
Unless, of course, you wat to make sure there's not another train on the same track or siding. Have you ever seen an overpass for trains, like you see for automobiles?
Trains wouldn’t use it for navigating, but for tracking and switching trains.