S. E. U. I. S. or Shoot'em Up in Space , is a squad-based tactical spacefight simulator.
The game allows player-vs-player and player-vs-computer gameplay. The player can play a pre-made introductory scenario, or can create their own custom galactic battles. At the initiation of a scenario, the player sets the strength of their individual squadrons, which are then assigned a position upon the galactic map. Players take turns moving their squadrons upon the galactic map, and squadrons that are located over individual planets will increase their resources each turn.
When two opposing squadrons occupy the same square, the game enters a real-time arcade-style combat mode. First, the player individually sets the firepower, shield strength, and rate of fire for each vessel. In this mode, each player controls one ship from the opposing factions. Extra ships will traverse the map at random. When two opposing ships come in close proximity they will fire upon each other. Combat is completed when one side has lost all of their vessels, and the losing squadron is destroyed. A campaign is ultimately won by destroying all opposing squadrons.
Custom scenarios allow the player to modify the starting map, as well as determine the number of starting squadrons and individual ship compositions.