The first Star Wars standalone movie, Rogue One, largely focuses on new characters, led by Jyn Erso (Felicity Jones) and Cassian Andor (Diego Luna). But it’s still chock-full of sly references to the larger saga, as it is sandwiched in between Revenge of the Sith and A New Hope in the series timeline. One of the most important of these references involves the little-seen upkeep of the only dark lord of the Sith, as Darth Vader’s introduction in Rogue One continues in the saga’s tradition of interwoven self-referential story beats.
Huge spoilers from here on out.
Imperial Director Orson Krennic flies to Vader’s castle on Mustafar to suck up to him about Tarkin’s hostile takeover of the Death Star project, but before he can put Krennic in his place with one of the sickest Star Wars puns ever (“Be careful not to choke on your aspirations”) he must be summoned from the ether of a bacta tank. These cylindrical tubes are meant to be kind of regenerative cure-all vessels. Quoth the Star Wars Databank entry puts it: “To promote healing, patients were completely submerged and used breathing masks while recuperating.”
When Rogue One takes place, Vader — formerly Anakin Skywalker — is naked, scarred, and missing a few limbs thanks to the longest and most boring lightsaber duel ever between he and Obi-Wan Kenobi in Revenge of the Sith that left him mutilated. The Vader in Rogue One is at his most evil without any real trace of Anakin left, and you can bet he gets some serious bad-guy-thinking done while in a nice meditative bacta bath. What a difference 19 years (within the series timeline) makes.
The image of a floating Vader was briefly seen way back in the very first teaser trailer, with the vulnerable Sith Lord flanked by two crimson Imperial guards and someone who we find out is his kind of Sith butler kneeling before him. The hint that it could have been Vader was given more credence by eagle-eyed fans pointing out that a creature featurette included concept art of a character without his limbs and seemingly breathing through some kind of apparatus that looked nearly identical to one seen in another Star Wars movie. It turned out to be true, and it gets at why Vader’s Rogue One bacta tank is so significant.
It is both a nice little precursor to his hyperbaric chamber later seen in The Empire Strikes Back, and a big elaborate version of the relatively modest one his son Luke was put in at Echo Base for a bit after being attacked by a Wampa on Hoth. It makes the bacta tank a kind of reverse echo that links Vader and Luke throughout the saga once more. They both get their hands chopped off, they both get tested by the Emperor on their way to being one with the Force, and now they’ve both spent some time recovering in a bacta tank. Father and son have shared very similar experiences through their Jedi-related journeys. One turned out to fulfill the prophecy of the Force and one didn’t.
Vader’s appearance in Rogue One isn’t given much context, and you really have to be aware of who he is in the other Star Wars movies to understand why he even shows showing up. He’s not the main bad guy, he isn’t behind any of the major Imperial actions in the movie, and he basically squabbled with Krennic about Tarkin’s power moves kind of in the same way he does in A New Hope. And yet his appearance is essential because of the small details, from his breathing suit, to his lightsaber, and even that bacta tank.