- "Never again will the Rebels leave you behind, looking flat-footed and foolish. The Immobilizer will see to that."
- ―Unnamed Sienar official
The Immobilizer 418 cruiser, also known as the Interdictor-class heavy cruiser, Interdictor-class medium frigate, Interdictor Dreadnaught, or simply the Interdictor, and sometimes colloqually as the Drag Ship, was a 600-meter-long cruiser built on the standard Vindicator-class heavy cruiser hull (later used for the Enforcer-class picket cruiser).
- "Awaiting your command."
- ―Unnamed Interdictor captain
The gravity wells mimicked a large mass in space and thus restricted hyperspace travel. Nearby vessels were automatically prevented from engaging their hyperdrive, and any ships passing through the area via hyperspace were forced into realspace.
As well as gravity wells, the Sienar design was also equipped with 20 quad laser cannons to combat starfighters. The Interdictor's hull was nearly identical to that of the Vindicator-class heavy cruiser and could support several additional weapons depending on mission profile. Such modifications (like those of the Corusca Rainbow, formerly the Black Asp) included the addition of ion cannons used to disable pirates and small craft attempting to flee. Enemy fire was absorbed by a deflector shield created by more than a dozen shield generators.
A variant of the Interdictor design existed, equipped with two large gravity wells rather than the usual four: a ship of this type appeared in Grand Admiral Thrawn's ambush of Luke Skywalker at Jomark in 9 ABY.
- "We need to take out that Interdictor before we can go anywhere."
- ―Anonymous rebel
The Immobilizer 418 was developed as a counter to the Rebel Alliance's hyperdrive-equipped starfighters in particular, and hyperdrive-equipped vessels in general. This was primarily to counter Alliance hit and run tactics, where a small group of starfighters or light starships would emerge from hyperspace, attack preselected targets, and re-enter hyperspace before sufficient force could be brought to bear on the raiders.
An Immobilizer at the site of attack, or able to access the area with a brief hyperspace jump, would be tasked to power up its gravity well projectors in an attempt to prevent the escape of the raiding party. Starfighter and capital ship support would then be used to eliminate the attackers, whose only options were to try to run for the edge of the interdiction field, or to attack the Interdictor and hope to inflict enough damage to disable the cruiser's influence. Either path would result in significant damage to the Alliance forces. It was only when they tried to escape into hyperspace that they realized it was an Interdictor. Interdictors could also be used when blockading planets or moons, such as Yavin 4.
Another duty of this class was to patrol trade routes. Freighters pulled out of hyperspace by an Interdictor would be in a position to have their cargo inspected. Interdictors were a welcome addition to the Imperial Customs assets, because while many smugglers and pirates wouldn't hesitate to outrun—or in some cases even outgun—an Imperial Customs Frigate, few would dare engage with a much more sizable Immobilizer 418, its gravity wells and its two squadrons of TIE starfighters. Interdictors assigned to Customs duties—such as the former Black Asp—would often have some of their quad lasers replaced by ion cannons so as to disable and capture any ship resisting inspection rather than destroy them outright.
Grand Admiral Thrawn was especially famous in connection with Interdictors for developing and refining a tactic that would be named after him—the "Thrawn Pincer" positioned the Interdictor's gravity wells along certain vectors. Other vessels—typically Star Destroyers—would be contacted, and would blindly execute a micro-hyperspace jump straight into the Interdictor's gravity wells, yanking them out of hyperspace near an enemy vessel. Much quicker than sublight movements, the Thrawn Pincer allowed reinforcements to be swiftly deployed on the battlefield and afforded a considerable element of surprise.
Although they were tremendous assets to any fleet, Interdictor cruisers suffered from some drawbacks. First and foremost, it took some time to power up and activate the gravity well projectors after the cruiser positioned itself and, once activated, the tremendous simulated mass they generated made the ship very slow and cumbersome to maneuver. While there was rarely enough time for an entire fleet to make the jump to hyperspace before a newly-arrived Interdictor activated its projectors, fast ships and starfighters could often escape to the edge of an active gravity well, and then make the jump to hyperspace.
The gravity wells were also a large drain on the ship's energy reserves, preventing the optimal use of weaponry and shields. This flaw was exploited on several occasions. When enemy ships were able to inflict significant damage to the Interdictor, the captain was forced to choose between entrapment of the enemy and his ship's own protection. This flaw was compounded by the fact that Interdictors were poorly protected and armed for a capital ship of their size. Enemy forces could send a smaller warship, such as an Nebulon-B frigate or Thranta-class War Cruiser to weaken an Interdictor's defenses and quickly force it to power down its gravity wells to fend for itself. Although the abilities of the Immobilizer 418 were fairly effective against the missile launchers of the Marauder-class corvette often employed by the Rebel Alliance, the ship was also known for its notorious weaknesses against larger capital ships such as the Mon Calamari MC80 Star Cruiser and bombers such as the BTL Y-wing starfighter.
Another problem was the fact that active gravity wells attracted space debris. An Interdictor could—and would—suffer external damage from larger pieces of such hazards. While most damage was minor—as the largest debris would be detected and fired upon by the gunnery crews—it was one reason Interdictors required more maintenance than many other fleet vehicles.[source?]
Additionally, the engine and hyperdrive-specific areas of an Immobilizer's interior sections were crewed only by maintenance droids, and were totally unprotected. Raiders and saboteurs were thus able to infiltrate and either disassemble or destroy the vital parts of the cruiser's propulsion systems.
Due to their importance and weaknesses, Immobilizer 418 cruisers were usually found on the periphery of the battle they were affecting, escorted by larger and better equipped capital ships and starfighters to protect them from harm and deliver the necessary damage.
While Sienar Fleet Systems' Immobilizer 418 was the most common design of Interdictor, other ships made use of gravity well projectors. Kuat Drive Yards used the hull of an Imperial-class Star Destroyer to create the Interdictor Star Destroyer which was supposed to compensate for the Immobilizer 418's combat weaknesses. The command ship used by Darth Vader immediately after the Battle of Yavin mounted large projector globes in the manner of the smaller cruisers.
During the Yuuzhan Vong War, the New Republic launched Mon Mothma and Elegos A'Kla, which carried improved interdictor equipment inside a normal Star Destroyer hull. The immense Eclipse-class and Sovereign-class Star Dreadnoughts also carried projectors internally within their massive hulls.
Interdictor technology was not completely limited to the Empire, however. Alliance forces made use of older CC-7700 frigates, and scientists in the Hapes Consortium reverse-engineered the gravity-well projector from captured ships; but rather than building bulky projectors, the Hapans fitted their Battle Dragons with launchers for charges known as pulse-mass mines, which produced much the same effect. However, pulse-mass mines could not be turned off or controlled like gravity wells, so this trapped the Hapans in the battle as well.
- "We're on the move."
- ―Unidentified Interdictor captain
The Interdictor cruisers were first manufactured by Sienar Fleet Systems two years before the Battle of Yavin. It was an Immobilizer 418 cruiser named Assessor that boarded Han Solo's Millennium Falcon, forcing him to jettison the glitterstim spice that he was smuggling for Jabba the Hutt and had the Falcon searched by Captain Tybert Capucot before Solo escaped once again from Imperial forces.
An Interdictor of the Imperial fleet was essential in the capture of Moff Kalast during the period of the Death Star construction. The Interdictor prevented the traitorous Moff's Star Destroyer from jumping to Hyperspace long enough for the Destroyer to be captured.
An Immobilizer 418 cruiser was responsible for the elimination of the Deretta Destroyers, an Alliance to Restore the Republic starfighter squadron, sometime before the Battle of Hoth. The squadron jumped into the target area of an Imperial depot ahead of their main Rebel strike force, where they softened up the opposition. However, the Immobilizer's presence prevented them from escaping, and the Destroyers were wiped out before the bulk of the Rebel force could arrive.
Between the Battles of Hoth and Endor, the Immobilizer 418 saw extensive action during the campaigns involving rogue Admirals Harkov and Zaarin and the threatened proliferation of TIE Defender technology. Aside from Thrawn, Zaarin was the only other Imperial officer to make frequent use of the Interdictor cruiser. Zaarin had the Harpago try to stop Darth Vader from warning Emperor Palpatine about the coup, then he deployed Grappler to trap Thrawn at the Rebel platform RS-32. In both instances, Zaarin's Immobilizer 418s were destroyed thanks to the intervention of Maarek Stele.
The Immobilizer 418 was prohibitively expensive, reportedly costing more than an Imperial Star Destroyer[source?], and produced in very limited quantities prior to the Battle of Hoth. By the time of the Battle of Endor, Sienar Fleet Systems had manufactured only a few hundred Interdictors;[source?] by comparison the Empire had approximately 25,000 Imperial Star Destroyers.
During the Hunt for Zsinj, Admiral Teren Rogriss moved his flag to the Interdictor Stellar Web and collaborated with Han Solo's fleet to trap and engage Warlord Zsinj's Iron Fist at the Battle of Vahaba.
These vessels would not realize their full potential until several years after Emperor Palpatine's death, when they became a key component in Thrawn's attempt to defeat the New Republic. The Grand Admiral, who commanded a large number of these ships in the Outer Rim Territories, would deploy them to ambush New Republic forces. He once used an Interdictor in conjunction with his flagship, Chimaera, in an attempt to capture Luke Skywalker. However, the Jedi eluded capture, by escaping Chimaera's tractor-beam lock, racing out of range of the gravity-well projector, and making a quick jump into hyperspace.
After Thrawn's defeat, New Republic technicians redesigned the Interdictor's gravity-well projectors, improving both their range and recharge rate. These new Interdictors, designated Immobilizer 418As, became one of the key components of the New Republic Defense Fleet during the Yuuzhan Vong War. During the Battle of Fondor, the New Republic supplied four Interdictors to the Hapan fleet.
One Immobilizer was used with other antique vehicles in the construction of the Hidden Temple used by the Jedi as a secret refuge during and after the Sith–Imperial War, and at least one was used during the Evacuation of Dac.
Behind the scenes
The Interdictor is almost always shown with its four gravity well generators represented by four complete globes, two on either flank of the hull. One early image of Thrawn's attempt to capture Luke Skywalker at Jomark, however, shows two hemispherical domes protruding along the centerline on the topsides, with two more by inference on the ventral hull.
While at odds with most subsequent representations, this rendering is as consistent with the original profile view in the Imperial Sourcebook as the more familiar four-globe variant, and another depiction of the same events at Jomark also shows the same distinct type of ship, this time seen from below—thus strengthening the claim of this type to be a canon variant rather than simply a visual inconsistency.
Some vessels such as Binder, Constrainer, and Sentinel were called Interdictors in the novels, and are presumed to be Immobilizer 418 cruisers. However, they were drawn as Interdictor Star Destroyers in the Dark Horse comic series.
In The Black Fleet Crisis Trilogy, an Interdictor starship was described as an Interdictor Dreadnaught. This ship was later clearly identified as an Immobilizer 418 in its entry in The Complete Star Wars Encyclopedia.
In the game Star Wars: Empire at War, the Immobilizer 418 is designated as a frigate, along with a wide variety of other ships smaller than Star Destroyers, and is armed with four laser cannons. The vessel is strong against Marauader-class corvettes, whose missiles it can divert, but is weak against larger capital ships and bombers. Additionally, The Official Star Wars Fact File lists the Immobilizer 418's length as 600 meters. However, this is inconsistent with the vessel's portrayal in Empire at War, in which the Immobilizer 418 is shown to be longer than the 752 meter-long Acclamator-class assault ship.
The 1998 PC program Star Wars: Behind the Magic includes a glossary entry for the "Interdictor-class cruiser." However, as this entry indicates, the description is intended to apply to the Immobilizer 418 cruiser. As such, that description should be not be confused with the Interdictor-class cruiser of the Star Wars: Knights of the Old Republic game. Star Wars: Rebellion: Prima's Official Strategy Guide likewise refers to the Immobilizer 418 cruiser as the "Interdictor-Class Cruiser."
The "Immobilizer 418" ship designation was used in the new canon, being mentioned briefly in the 2014 James Luceno novel Tarkin. The Immobilizer 418's appearance in Legends was given to the Interdictor-class Star Destroyer in the new expanded universe