In 1981, Midway released the space-shooting game Gorf. Known for its use of synthesized speech, Gorf was also the first game to feature distinct levels of play. The five levels of Gorf are essentially five unique games. The first level- Astro Battles- consists of a Space Invaders-like scenario in which the player must kill enemy aliens marching from the top of the screen. In the second mission- Laser Attack- players fight against squadrons of laser-beam-firing, dive-bombing spaceships. The third mission is called Galaxians and is a clone of Galaxian in which players fight against an array of attacking aliens. The fourth level- Space Warp- has aliens attacking out of a wormhole. In the fifth and final mission- Flag Ship- the player must defeat the Gorfian Flagship by hitting the ship's reactor core. Gorf was ported to the Atari 2600, Atari 5200, ColecoVision and the personal computers Commodore 64 and VIC-20. To avoid licensing issues, the name of the Galaxians level was changed.