In Rogue One: A Star Wars Story, the Rebel Alliance is up in arms over the Empire’s willingness to use a weapon of mass destruction called the Death Star. The movie did a good job at demonstrating the planet-killing evil of the Empire and the moral ambiguity of the Rebels, but failed to mention another Star Wars superweapon that has been hiding in plain sight since the original trilogy. It’s called an ion cannon and basically, it’s a device which is the Star Wars universe equivalent of weaponizing an electromagnetic pulse. But the most surprising thing about it is that it has belonged to the Rebellion this whole time.
In The Empire Strikes Back, Princess Leia gives the troops a pep talk and explains exactly how everyone is going to get off of Hoth. After a pilot meekly points out that two fighters against a Star Destroyer isn’t going to cut it, Leia responds, “The ion cannon will fire several shots to make sure that any enemy ships will be out of your flight path.” Wait. What? The Rebels just have an awesome cannon that can take out giant Imperial vessels? I’m not talking about the local bulk cruisers, mind you, these are the big Corellian ships. If the Rebels have this kind of weapon, what chance does the Empire have?
According to the original script for The Empire Strikes Back, the effect for the ion cannon was supposed to look something like this: “As the Rebel transport races toward the waiting Imperial Star Destroyer, it is overtaken by the two scarlet energy bolts. The Imperial Star Destroyer is hit in the conning tower by the powerful bolts, which set up fiery explosions on its metal hull.” But in the final film, this isn’t what happens exactly. Instead, the bolts from the ion cannon seems to short-out the Star Destroyer, as though all of its electricity stopped working instantly.
For anyone who’s played the old ‘90s Star Wars video games from X-Wing to Rogue Squadron, this is old news. The Rebels use big ion cannons on Hoth, but tinier ones on their ships, like the Y-Wings. The official Star Wars databank defines ion weapons thusly: “Ion weapons fire ionized particles that disrupt electronic systems. These weapons range in size from Jawas’ custom ion blasters, used to disable droids, to massive cannons that can turn starships into silent, drifting hulks.”
Chronologically, Star Wars.com maintains ion cannons first showed up during The Clone Wars, though the technology appears to have persisted well past that point. In fact, the entire Battle of Scarif in Rogue One hinges on the ion cannons on the Y-Wings disabling one of the Star Destroyers, which allows for it to be pushed around by the Hammerhead Corvette at the last minute. To be clear: What happens to the Star Destroyer in Rogue One looks very similar to what happens to the Star Destroyer in The Empire Strikes Back. Meaning, without the ion cannons, there would be no way to disable the Star Destroyer above Scarif, and the destruction of the shield gate wouldn’t have happened. So, both the Battle of Scarif and the evacuation of Hoth were mostly successful Rebel operations and wholly dependent on the possession and use of an ion cannon. The new U-Wing ships in Rogue One have ion cannons, too. This partially explains why the modified AT-AT walkers in Rogue One seem easier to take down than the ones in Empire. The U-Wings are disrupting all the electronic systems on the AT-ATs, making them, like the Star Destroyer that gets rammed in orbit, easier to deal with.
The real equivalent of this kind of “electronic disruption” technology is called an EMP (electromagnetic pulse). In the real world, taking into consideration that different voltages have different effects, a high enough voltage EMP can disable electronic equipment and instruments. In this way, the Rebel Alliance is weaponizing the same natural thing that happens when an electrical lightning storm messes with phone reception.
Knocking out a bunch of electricity in a localized area is often used in other sensational fiction. The James Bond movie GoldenEye posited a satellite in orbit could deliver such a pulse and send modern cities into the dark ages. In reality, the scale of this EMP would have to be created by a nuclear detonation. At least, that’s how it would work in our galaxy. It’s unclear if the ion cannon disruptions in Star Wars operate on the exact same principles as an EMP would for us. It’s also similarly unclear if the Rebel Alliance — or extremist factions — would use ion cannon-type weapons to knock out electrical functions in more than just military targets. Instead of a Death Star, the Rebels have the technology that a Bond villain might use to hold an entire city, or planet, hostage. Anyway you look at it, its an insidious weapon that the Rebels just casually have.
After losing several Star Destroyers because of the EMP devastation brought on by the ion cannon, you’d think the Empire would get their shit together. Why build a planet-destroying Death Star when the technology to simply make everyone’s spaceship stop working is right there at your fingertips? Then again, the Empire never was very practical. But the shortsightedness of the Rebels is on display here, too. If one ion cannon could knock out a big Star Destroyer, could several have disabled a Death Star?
In Return of the Jedi, the Rebels don’t use ion cannons, which seems like a Death Star-sized plot hole. Because if Jawas can obtain low-level versions of this tech, there’s no reason why building more ion cannons — a weapon that served the Rebellion very well — wouldn’t have been made top priority. Who knows, maybe the Rebels felt guilty for all that electricity they disrupted.