Decwar

The original game that led to DECWAR was WAR, a two-player version of Star Trek for the CDC 6600. In Star Trek, a single player would hunt around the galaxy looking for an invasion force of Klingon warships, and return to a number of starbases to refit and repair. In WAR, the starbases were replaced by planets that either player could capture after attacking them, turning them "friendly". The game ended when one user captured all of the planets and destroyed his opponent's ship. The 6600 supported only one operating terminal, so the players had to take turns entering their commands.

During a port to the PDP-10 (also called DECsystem-10), the game was more heavily modified and became DECWAR. The game was no longer run as a single instance, but instead as a number of programs (or "jobs"), one for each user, communicating through a shared memory. This allowed up to 18 players to join or leave the game as they wished, the other players continuing to see the map as it was before. Another addition was a single computer-controlled Romulan ship, who would be spawned into games with less than full players in order to give the humans someone to fight. When the roster filled with players (the number depended on the version) the Romulan would not be re-spawned after being killed.