Get rid of AI troops completely, and require say... 3 player troops to take a base.
These would have to be DEDICATED troops, no bailing out of planes.
So, one C-47 pilot drops 3 real live players, they have to land and run to the map room.
How they get there is up to them.
Same thing with M3, Jeep (although you'd have to knock down the number of people a Jeep could carry).