Destroy bullet fired by alien ship.

Destroy an alien ship with left turret.

Destroy an alien ship with center turret.

Destroy an alien ship with right turret.

Destroy alien ship dropping power up

Collect ammo power up.

Destroy half the alien ships in game.

Score 50000 points in game.

Complete mission with at least 2 turrets left.

Complete mission with at least 2 cities left.

Complete a level by destroying all alien ships.