Space Invaders is an arcade game. It is a 2D horizontal shooter where the player controls a cannon by moving it across the bottom of the screen and firing at a swarm of aliens. Points are earned for every alien it shoots down. A UFO will occasionally move across the top of the screen and award bonus points if destroyed. As more aliens are defeated, the game speeds up. The aliens also fire shots randomly as they approach the bottom of the screen, and If the shots hit the player, he loses a life. The cannon is partially protected by several bunkers that are gradually destroyed by numerous blasts from the aliens or player. Defeating all the aliens brings another wave and repairs all bunkers. The game ends if all bunkers get destroyed or the aliens reach the bottom, or if the player loses all lives.