It was called Defcon 5. It was a horrible doom like game, but you had to defend your base against incoming enemy ships with these huge guns mounted on your base. It was really a stupid game. The worst part was having to travel in your base. You rode on these train like things, but everytime you rode one, it would cut to a cut scene of the train zipping around the base. It was so lame.

Yeah, it must have been an earlier one. It was one of the first games I bought for it. One of those things where I was like, it looks cool, I take it! I regret that decision still.