Vagaari ship net

Ship nets were what the Vagaari called the gavity projectors used to keep enemy ships from escaping to hyperspace. They were carried in the Vagaari ships in a collapsed position and, when they deployed, would take on a spherical shape. They would then produce gravity similar in magnitude to that of a planet. This mass shadow would cause ships to be unable to jump to hyperspace. It would also cause any ship crossing its path in hyperspace to be yanked back into real space. While it is possible the Vagaari created this technology themselves, it is more likely that they stole it from another race in the Unknown Regions, as was the case with most of their technology.

Thrawn stole one of these Ship nets and used it to trap a Trade federation task force, the Outbound Flight, and the Vagaari Fleet themselves. Due to Thrawns tacticle genious and their inability to escape, all three groups were crippled or distroyed. Presumably, Thrawn later handed the ship net, along with the remainder of the defeated Vagaari fleet over to the Chiss government for study and reverse engineering.

The Galactic Republic (later the Galactic Empire) was familiar with the theory behind gravity projectors (usually called Interdiction fields), having possessed less powerful versions of this technology a mellinium before (Leviathon). But with the advancement of modern hyperspace engines, the old interdictor technology was largely inneffective. The interdiction field generators necessary to pull modern hyperdrives out of hyperspace required to much energy to be practicle. The Vagaari ship net design found a way around the power consumptions issues.

Interdictors were used by Thrawn while he was a Grand Admiral in the Galactic Empire. Thrawn's information on the Vagaari ship nets may have been the basis for Imperial Interdictor technology. That technology was later passed to the Galactic Alliance and the Hapes government.

Behind the scenes
Interdictor technology plays a heavy role in most of the novels writen by Timothy Zahn. Interdictors were first used by the Empire in his Thrawn Trilogy. In his "prequel" Outbound Flight he discribes Thrawn's first obtaining the technology (from the Vagaari.  In the books, it is discribed as new technology, however, the technology appears in Knights of the Old Republic]], which taked place 1000 years before the Thrawn books.  This is retconned by the star wars Database by indicating that the interdictors in the KotOR time period are far less powerful, and no longer effective in the Empire's time period.

Like Cloaking technology, Power consumption is indicated as a major limiting factor to interdiction fields in the Zahn books.

Scources
*Outbound Flight (novel) *Leviathon on the Star Wars Database