By chance the empire revealed my rebel base by putting leader there with mission and gaining loyalty but did not have troops set up to take it. I used rapid mobilization to move base from my understanding none of the units you have on rebel base space get moved to new base? The imperials attack the system the base anyway , so do the units from the rebel base space get put on the system where the rebel base used to be ?

As soon as the base is revealed all units on the "rebel base space" get moved to the system where the base is.

As long as the base is revealed, you cannot put units on the rebel base space

If you move the base, the units all stay on the planet the original base was on, but you can again start building units on the rebel base space as it is now hidden again.

Ok thats how i played it just wanted to make sure thanks

Oooh I didn't realize the units stay behind. What if I move base locations while the base is still hidden? Do the units on the base remain on the origial planet and reveal themselves?

I'd have to double check the rules on that one, but I think when you are moving the base, the first thing you do is reveal the old one, which would trigger the units being shifted onto the planet before you actually establish a new base. So yes, the units would stay behind.

Oooh I didn't realize the units stay behind. What if I move base locations while the base is still hidden? Do the units on the base remain on the origial planet and reveal themselves?

Yes. You reveal the base to the Imperial player, place the troops in the system on the game board, and then select a new hidden base by drawing cards from the probe deck. The Rebel base will be empty until units are moved to or built there.