Military is deploying own portable - well they are big like a vehicle - nav aids. And yes, INS/GPS - you just replied to your own question. INS are updated on the apron or inflight corrected with military GPS signals. And yes, stars are used too and flying navigators were trained to navigate by stars - it is last resort though. However there won't be many constant signal emitting navaids available, and usually far away from the front line. The ones used by military will switch on and off only for mission purpose, right? Although one can expect portable TACAN near the airfields visited by US aircrafts.