Free Space Available military flights via Air Mobility Command, formerly Military Airlift Command (MAC), within the continental U.S. and Europe and Asia.  The flights are from base to base.  The schedule changes as the requirements change.  Aircraft are usually C-9, C-141, or C-5s with airline seats, or sometime C-130s with jumpseats.  Within the continental U.S., active duty members, military retirees, and reservists (no dependents) are eligible to fly.  Overseas, dependents are allowed to travel with their military member.  You can sign up ahead of time online.