Alien Invaders

Alien Invaders is a variant of Space Invaders . A 14x5 rectangular formation of enemy spacecraft appears from the top of the screen, and slowly gets closer to the surface of the Earth. You control a mobile missile launcher that can shoot up at the invaders, while the aliens try to bomb you.

As in Space Invaders, there are fortifications which can give you some shelter from the bombs, and these are slowly worn away as they are bombarded. There is also an enemy mother-ship that appears overhead, which gives you bonus points. But unlike Space Invaders, there is only one wave.