Defender was released circa February 1981 by Williams who also developed the game. Defender is a shoot’em-up arcade game.

Defender is a two-dimensional side-scrolling shooting game set on the surface of an unnamed planet. This game really developed the genre of side scrolling games for many years.

The player controls a space ship as it navigates the terrain, flying either to the left or right. A joystick controls the ship’s elevation, and five buttons control its horizontal direction and weapons.

The idea is to shoot the alien invaders while protecting the astronauts below. The game is more or less Space Invaders sideways.

The game has several levels that get tougher as the game goes on.

Failing to protect the astronauts, causes the planet to explode and the level to become populated with mutants. Surviving the waves of mutants results in the restoration of the planet.

Players get 3 ships and when they run out its game over.

The game uses the 6809 CPU for graphics and gameplay, A second 6800 CPU was used for audio. The 16 color CRT was standard 320×256.

The game was slow selling at first but went on to sell 55,000 units.