Centaurians

Centaurian Scout   Unarmed but somewhat dangerous, they will attempt to destroy you by crashing into your ship.

Elite Centaurian Scout  More maneuverable and quicker than their red cohorts, they are  more dangerous.

Centaurian Fighter  Armed with deadly projectiles and heavily armored, these ships are fast and deadly.  Expect them to take several hits to destroy and to pursue you mercilessly.

Gomer  No one knows whether these massive metallic objects are machine, organism, or some combination.  They are fast and heavily armored.  IGSF scouts report that they either close quickly or oscillate depending on what direction their target is moving.  No explanation for this behavior is forthcoming.

Spy Ship  These vessels don't usually attack.  Instead, they make close passes, presumably to observe invaders.  All of them seem to carry bits of Earth technology, so if you destroy one of these, look for useful items amidst the debris.  Don't use heavy weapons on them or you're likely to destroy the salvageable items along with the ship.