Got to a command post with the life support systems go to the part with the kamionan chairs there you should see an ammo and health droid jump on them and you MAY fall through the floor and you will be able to kill enemy units through the floor.

NOTE: I was only able to fall through the floor three times and it took me about 4 minutes to fall and i died one time of the three.Also note that there is more than one way to fall through the floor