System patrol craft, sometimes known simply as patrol craft, patrol ships or patrol vessels, were combat warships designed to operate within a single star system, serving a dual role as customs ships and defensive pickets. Usually deployed from surface bases or carriers, they were in effect the sublight, defense-oriented equivalent of .
Under the Galactic Empire, systems patrol craft were defined as capital ships without hyperdrives, measuring between 100 and 250 meters in length and with a crew of between four and twenty: a typical example was the IPV-1 produced by Sienar Fleet Systems. Fast and maneuverable, these ships were designed primarily to catch and overpower fleeing ships—especially smugglers—before they could make the jump to lightspeed, but their impressive sublight speed also enabled them to intercept attacking forces as they arrived in the star system they were guarding. In such situations, they were capable of skirmishing with small capital ships up to the size of frigates and corvettes, although they were not agile enough to dogfight with starfighters, or powerful enough to take on cruisers.
Not all ships serving as system patrol craft conformed to the standard parameters, however. Older, larger ships were sometimes deployed by Imperial commanders where it was not possible to assign a proper modern patrol craft, and by the time of the New Republic, the Corellians had developed the Mynock-class assault boat, carrying heavier weaponry and a larger troop compliment on a slower and smaller—but nevertheless hyperdrive-capable—hull, more useful for ground assault and boarding actions than in the traditional interception role.