hey
i know where ive seen this...
Future Cop LAPD for the PSX
You both have a base and CPs which have big guns. For holding them you can build tanks. choppers or super tanks which then leave your base and head for the enemy base to blow the base up.
If I remember, you yourself cannot get to the enemy base to destroy it so you have to defend your tanks heading to it, or defend your base from the enemy tanks.
Is that where your idea came from? as i remember playing that. In fact that was the best ever game in the world for a MP mode.
Edit:
woo. found a pic of you buying tanks to attack enemy base. (Now those are 1337 gfx)
some more pics here if you need any
http://www.mobygames.com/game/shots/gameId,3628/