Most appearances of Interdictors in the Star Wars universe are in Legends and are therefore non-canon. However, they do make an appearance in the [canon novel *Tarkin*](http://starwars.wikia.com/wiki/Tarkin_%28novel%29). At the time ([about 17 years before the Battle of Hoth](http://starwars.wikia.com/wiki/Timeline_of_canon_media)) the ships were experimental and did not function well. They were used in an attempt to recover Tarkin's stolen ship, the *Carrion Spike*. Here is the relevant quote from the book (with some emphasis added), which includes their introduction and use:

> “By utilizing Interdictor cruisers, my lord -- precisely placed to yank the *Carrion Spike* from hyperspace short of its destination system and reversion point. Governor Tarkin assures us that any jump from the dissidents’ current location will require at least two reversions to reach potential Imperial targets. Thus, Interdictors can be positioned in advance of the Carrion Spike’s arrival.”
>
> The Emperor looked down at Kren Blista-Vanee.
>
>“The requested Interdictors are being developed as part of the Deep Core Security Zone, my lord.” Fond of wearing flamboyant hats and frequenting the opera, Blista-Vanee was a relative newcomer to the Ruling Council, but had already proven an asset in blazing hyperspace routes into the Deep Core star systems. “I hasten to add, however, that **the ships’ gravity well projectors have not been tested in scenarios of this sort.**
>
> ...
>
> Tarkin angled the microphone of his headset closer to his mouth and opened the battle net to the task force liaison officer, who was aboard the [CC-7700 frigate](http://starwars.wikia.com/wiki/CC-7700_frigate).
>
> “The projectors are powering up to high gain, Governor Tarkin,” the commander said. **“The field will be initiated, then disabled, in an effort to keep from dragging vessels other than the quarry from hyperspace. I should caution, however, that that may be unavoidable, given the heavy traffic in this system.”**
>
> “I understand, Commander,” Tarkin said. “Order your technicians to be judicious, nonetheless.”
>
> “I will, sir. But the power setting of the gravity wells is dictated to some extent by the relative speed of the targeted ship, and, well, sir, to be blunt about it, there aren’t many as fast as the *Carrion Spike*.” Tarkin pinched his lower lip in thought. Ideally, local systems would had been notified that Obroa-skai had been designated a no-entry zone, but naval command had opted against issuing the designation for fear of alerting the dissidents. He had other reasons for concern: chiefly the question of why the dissidents would jump to Obroa-skai, which lacked anything in the way of an Imperial target, and was known mostly for its medcenters and libraries.
>
> “T minus thirty and counting,” the specialist in the data pit announced.
>
> Moving to the forward end of the walkway, Tarkin fixed his gaze on the trio of Interdictors. Arms folded across his chest, he counted down in silence even while the voice of the specialist was doing the same in his right ear bead.
>
> **The countdown had just reached T minus five when Tarkin was yanked forward, nearly completely off his feet. Fearing another lurch he spread his hands wide and so was kept from being slammed headfirst into the closest viewport panel. Klaxons began to howl throughout the suddenly trembling command bridge as the giant ship groaned and lurched yet again in the direction of the distant Interdictors. Struggling to remain upright, Tarkin caught a glimpse of the middle-distance frigates and pickets being pulled forward, almost as if accelerating.**
>
> “Commander,” he shouted into the headset mouthpiece, “the field is too powerful!”
>
> “Working on it, sir,” the commander said with equal volume. “It’s the Immobilizer. The overcurrent resistors failed to prevent the gravitic systems from redlining—”
>
> The comlink connection broke.
>
> Close to the Interdictors, ships began to appear where there had only been star-filled space. Tarkin turned from the forward bay and stumbled back to the data pit to study the magnified view on one of the screens. First to drop out of hyperspace was an outmoded, saucer-shaped YT-1000 freighter, followed by two angular transports and a lustrous space yacht. Then another freighter winked into visibility, followed by two passenger vessels.
>
> **Abruptly, Tarkin felt as if he’d been shoved toward the rear of the bridge. With the interdiction field neutralized, the ships that had been caught in the invisible web began to whirl out of control. Two of the ships collided and drifted out of view. The magnification screen showed the sublight engines of other ships flashing, but the ships barely had a chance to flee or correct their spins when the field re-initiated, capturing them once again. Tarkin spread his legs wide in an effort to balance himself; then his eyes went wide as well as he turned to face the viewports. Listing on its port side, an enormous ship that more resembled something grown than built decanted, broadsiding the Detainer CC-2200 before careening into a spin that left its dorsal surface impaled on the Interdictor’s sloping bow.**
>
> “Mon Cal star cruiser!” a voice in his ear said, loud enough to be heard over the head-splitting racket of the klaxons. “The luxury liner *Stellar Vista* out of Corsin. **Approximately ten thousand aboard!**”
>
> A brief but nova-bright explosion flared in the distance, ferocious enough to leave Tarkin blinking and seeing stars that weren’t there. When he was able to focus through the viewport’s blast-tinting, **he saw that the stern of the organically sculpted passenger ship and disappeared and that the Interdictor had been knocked ninety degrees from its former position. In moments podlike lifeboats and flocks of spherical escape pods were streaming from the stricken liner.**
>
> **"The *Stellar Vista* reports that it is in imminent distress," the specialist said. "The ship's captain is requesting all the help we can provide."**

The Interdictors worked, but they nearly created more problems than they solved. Presumably, the Empire could improve the gravity well generators in the 17 years between this incident and the Battle of Hoth, but the incident may have caused the Empire to completely abandon the use of Interdictors. As the Empire tightened its control on the galaxy, Interdictors may have been considered not worth the trouble of development. We can only speculate why the Empire did not include Interdictors at the Battle of Hoth, but this incident provides some reasons why the Empire would avoid using them (and perhaps abandon them entirely):

 - The gravity well generators were difficult to control.
 - The interdiction field posed a danger to Imperial vessels (including the Interdictors themselves) and personnel if not properly controlled.
 - The interdiction field would drag civilian vessels out of hyperspace and into a battle.
 - Civilian vessels were damaged in this incident, creating a public relations problem for the Empire that interfered with further development.

(Out of universe, Interdictors weren't present because they hadn't been invented when Episode V was released.)