Warning: Mild spoilers for the Season 3 finale of Star Wars Rebels, 'Zero Hour', to follow. Proceed with caution!
The Season 3 finale of Star Wars: Rebels was full of thrills and spills, pitting our heroes against the strategic brilliance of Thrawn. As I've discussed in an earlier post, it was very much a homage to The Empire Strikes Back; the Empire discovers a Rebel base and attacks in force, with the Rebels hiding behind a shield while they prepare for an evacuation. But here's the catch; as great a homage as 'Zero Hour' may have been, it introduced one tiny problem...
Why Wasn't There an Interdictor at Hoth?
Introduced in the old Expanded Universe, and gradually imported into the new canon, Interdictors are sophisticated cruisers that create an artificial gravity shadow. Because Hyperspace travel is warped by gravity, an active Interdictor essentially generates a bubble around it — one where you can't jump into Hyperspace. Worse still, if you're traveling through Hyperspace and hit the mass shadow of an Interdictor, you'll be pulled out; you won't be able to return to Hyperspace until you get out of range.
Thrawn uses two Interdictors at Atollon, ensuring the Rebels can't escape.That said, his strategies go wrong when Admiral Konstantin proves too head-strong, and one of the Interdictors is taken out. Mandalorians later arrive to neutralize his second Interdictor, and the Rebels escape.
But let's face it: this Interdictor technology is very, very dangerous. Why didn't Darth Vader use an Interdictor at Hoth? Had he done so, the Rebel vessels wouldn't have been able to flee; I'm sure the Millennium Falcon would still have escaped, but I doubt many others would have had the ingenuity and piloting skills of Han Solo. Of course, the out-of-universe reason is that #GeorgeLucas didn't dream up the idea of Interdictors back in 1980 — they were created by Timothy Zahn in the 1990s. But the Lucasfilm Story Group is otherwise exceptional when it comes to charting a single, consistent line of continuity through the Star Wars universe — by using Interdictors, have they unwittingly created a major plot hole?
The Technology is Associated with Thrawn
The first thing that's worth noting is that the technology is traditionally associated with Thrawn. In the old Expanded Universe, Thrawn discovered the technology while policing the Unknown Regions on behalf of his race, the Chiss. It didn't take him long to develop strategic uses for the Interdiction technology; within just weeks, he was plotting Hyperspace routes between opposing forces, and using a well-placed Interdictor to bring them into head-on conflict. When Thrawn eventually joined the Empire, he brought some of the basic principles of Interdictors with him, and the Empire reverse-engineered the idea based on Thrawn's observations. We can presume it's no coincidence that Star Wars: Rebels has tied Interdictors and Thrawn together in this way; it seems that connection is being kept in the new canon, and will likely be explored in Timothy Zahn's next novel, Thrawn.
Here's the catch; it's entirely possible that not many other Imperials appreciate the strategic value of Interdictors. After all, even in 'Zero Hour', we saw that Konstantin lacked the tactical skill to understand how an Interdictor's presence changed the nature of battle. When an Interdictor is in play, the whole battle winds up revolving around it; if the Rebels don't destroy the Interdictors, then they're trapped. In strategic terms, only the more intelligent and creative commanders will be comfortable with the use of Interdictors. I can imagine Thrawn as one of only a handful who are interested in experimenting with them.
Interdictors May Not Be Reliable
At the same time, though, the new Star Wars canon has gone to great trouble to ensure we understand the risks of using Interdictors. They were first brought into the new canon in James Luceno's novel Tarkin, which showed just how badly wrong early experiments with Interdictors could go:
"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."
Interdictors are blunt instruments, and an ill-placed Interdictor can easily cause major disasters. All you need is for two ships to unexpectedly revert from Hyperspace and collide — and if those are civilian ships, perhaps even passenger vessels, then there can be an horrendous death toll. As you can see from the Tarkin excerpt, these disasters easily result in an Interdictor's destruction.
Worse still, an earlier episode of Rebels, 'Stealth Strike', showed how easily a gravity mass projector can go wrong. In that episode, the Rebels sabotaged the Interdictor, with the artificial gravity ultimately leading to the vessel's own destruction. I can't help wondering how many prototypes were lost, and how many disasters were caused while Interdictors were experimented with.
Ultimately, it seems that at least in the new canon, Interdictors are used sparsely. The technology can easily go wrong, with terrifying results; I'm sure 'Stealth Strike' wasn't the only example of Rebels sabotaging an Interdictor. What's more, few Imperial military leaders would feel comfortable with the use of Interdictors, resulting in simple and costly mistakes, as we saw in 'Zero Hour'. It's possible that, by the time of Hoth, the Empire had abandoned them altogether.