On Thrawn's career in Imperial Navy and flagships (LEGENDS)
So, here’s the most in-depth analysis of Thrawn's career in the Imperial Navy in old Legends canon I could come up with, while also keeping track of all the ships under his command.
The following insight takes into consideration the years from 19BBY to 8ABY (the Thrawn campaign is not included here).
Early service
Thrawn joined the newborn Empire in 19BBY. We don’t have many infos about his first 18 or so years of service, we do know he rose quickly through the ranks and that he mostly operated either in the core or at the borders with the Unknown Regions, Uwlla Iillor served under him there. We also know that he explored the planet Nirauan and established his base of operations in what will become the Hand of Thrawn fortress very early in his imperial service.
We do know that he at some point achieved the rank of Colonel:
«Iillor had been sent to serve under Colonel Thrawn and a host of other alien superior officers before she had been given a ship of her own.» X-Wing Rogue Squadron, Michael A. Stackpole, 1996
It’s a bit difficult to understand how he could be a Colonel since it is a field rank and we know for sure Thrawn’s always been in the Navy.
Now, the only branch of the Navy to use Army ranks are the Starfighter Corps, so was Thrawn an executive officer in the Starfighter Corps? That’s my best assumption. I mean, he does like running around in a stormtrooper armor… but I don’t think that’s the case ^^ And the thing suites him considering how he always showed particular recognition for starfighter pilots.
Line Captain
In 1BBY we meet him with the rank of Captain aboard what it is safe to assume is the first capital ship he was assigned command of: the ISD Vengeance under inquisitor Jerec (EDIT: no, she was not. If he was a Senior Captain in the Kaleesh-Imperial conflict he definitely was in command of other capital ships before the Vengeance). This is stated in Dark Force: Soldier for the Empire (William C. Dietz, Dean Williams, 1997):
«Captain Thrawn stood behind Jerec, slightly to his right. (…) much as Palpatine might distrust other sentient species, he loved a winner, and Thrawn had collected more victories, medals, and promotions than most officers with twice his years of service.»
EDIT: We do not know the exact moment he achieved the rank, but we do know that he was tasked with the pacification of the Fringe and around 6BBY he spearheaded a major offensive against the Kaleesh that brought to the near extermination of the Kaleesh people and the destruction of planet Oben. This is first hinted at in Heir to the Empire (Timothy Zahn, 1991):
«“Isn’t it?” Thrawn agreed, his voice sounding almost wistful. “It was my one failure, out on the Fringes. The one time when understanding a race’s art gave me no insight at all into its psyche. At least not at the time. Now, I believe I’m nally beginning to understand them.” “I’m sure that will prove useful in the future,” Pellaeon offered diplomatically. “I doubt it,” Thrawn said, in that same wistful voice. “I wound up destroying their world.”»
The bombardment of Oben in early 1BBY marked the end of the conflict. We know Thrawn was a Captain then, and we can safely assume he was a Senior Captain for he was in charge of a fleet:
Bentilais san Sk'ar joined the Empire after a Star Destroyer fleet commanded by Captain Thrawn leveled his planet when the Imperial officer failed to comprehend Sk'ar's people by studying their artwork. (Aliens in the Empire, Part 2: To a Traitor Go the Spoils, Hyperspace, 2007)
That means sometimes before 6BBY he got transferred into the Navy's naval forces, and thus assumed the Colonel's equivalent rank of Line Captain. (end EDIT).
In Rebel Force: Target (Alexander Wheeler, 2008) set two weeks after Yavin, he’s again referred to as Captain Thrawn. Yet it is stated very clearly that his influence is much bigger than that of a simple captain. He’s one of the lowest ranking officers present at the Death Star fiasco emergency meeting:
«Ten of the most powerful men and women in the galaxy faced the Emperor, fear rolling off of them in waves. (…) Captain Thrawn betrayed no emotion. Complete control, the Emperor thought with approval. This one will go far.»
Commander of ISD Admonitor
We then know that 8 months after the Battle of Yavin, Thrawn is the commander officer of the ISD Admonitor and the Admonitor Task Force and as such holds the rank of Line Captain or Senior Captain. This is stated in Choices of One (Timothy Zahn, 2007):
«As the Admonitor intensified its fire the alien ships ickered with the pseudomotion of a hyperspace jump and vanished. “And that,” Odo said, “is that. Senior Captain Parck, are you still there?” “I am,” Parck said. “Thanks to you. One correction: I’m merely Captain Parck. My superior, Senior Captain Thrawn, is currently away from the ship.” Pellaeon felt his back stiffen. This was Thrawn’s attack force?»
It is also pretty obvious that his Senior Captain commission and the command over the task force are directly linked. Task force that was originally composed by the Admonitor alone but we do know that the Emperor steadily provided Thrawn with more ships, Victory-class Star Destroyer Iron Fist, responsible of the destruction on planet UR41-284 in the Unknown Regions, was one of those.
Yet in Galaxy of Fear: the Swarm (John Whitman, 1997), set 9 months after Yavin, Thrawn is still in command of the Vengeance and holds the rank of Captain (EDIT: he's addressed to as captain, but his rank is most certainly Senior Captain) (It is also worth noting that on the cover of the book he wears a white uniform with a, err, questionable rank insigna and he gets called “General” at some point XDDD).
Not a very faithful Thrawn, but a pretty cool one 8)
We also know he taught at the Academy for a certain period and this happened when he was captain of the Admonitor (Star Wars: Empire at War: Forces of Corruption, 2006).
Ok, so up until now things are pretty linear. You following me? Good, ‘cause now things start to get messy… basically because Timothy Zahn retconned himself. More than once (thank you -.-).
It is stated in Vision of the Future (Timothy Zahn, 1998) that:
«“Niriz was the captain of the Imperial Star Destroyer Admonitor, which Thrawn took back into the Unknown Regions on his supposed mapping expedition a few years later.”»
Now, this is not possible for we know that Thrawn was the original captain of the Admonitor as Zahn himself says in Choices of One (see above). Granted, this is a retcon that comes a decade later, but I take Choices of One as the most reliable source as it is the most recent.
According to this, Dagon Niriz could have become captain of the Admonitor after Thrawn was appointed Admiral.
Admiral and the Emperor's "mapping" mission
We learn from Command Decision (Timothy Zahn, november 1996) that in 2ABY Thrawn is an “Admiral”.
Though, what kind of admiral is difficult to tell: the term is used to address every officer from Rear Admiral to Grand Admiral, but in the official art from Star Wars Adventure Journal #11 Thrawn’s depicted with the grey uniform and the plaque of Fleet Admiral (with inverted colors) on his chest. Same happens in X-Wing Rogue Squadron #25 (december 1997) where Thrawn appears in flashback wearing a Fleet Admiral insigna:
Admiral Thrawn from Star Wars Adventure Journal #11 and from X-Wing Rogue Squadron #25
This flashback recalls the Battle of Derra IV which happens in 3ABY (between 38:3:31-6:7), so we know that at the beginning of 3ABY he is still an admiral.
It is also in 2ABY that, despite having operated on the borders of the Empire for the most part of his career, he starts the extensive operations to bring part of the Unknown Regions under Imperial control. Operations he carries out in secret under the cover of a "mapping expedition". We know it's 2ABY from Command Decision:
«Now, with this final jump, the Imperial Star Destroyer Admonitor had left even that behind. Ahead of them lay the Unknown Regions. Behind them lay the Empire. And, for all practical purposes, the ruins of their careers.»
Later in 2BBY Thrawn returns from the Unknown Regions to aid Darth Vader in dealing with the Black Sun on Corellia. He takes along Cpt. Niriz and the Admonitor as it is narrated in Side Trip (Timothy Zahn, Michael A. Stackpole, may 1997). Yet he is now somehow a Grand Admiral…? 🤷🤷
«"I hope so, sir," Niriz said, his stomach tight with concern as he gazed at those glowing red eyes. "Admiral...I have to say one last time that I don't think you should do this. At least not personally." "Your concern is noted," Grand Admiral Thrawn said, running a gauntleted hand through his blue-black hair. "And appreciated, as well. But this is something I can't delegate to anyone else."»
In Star Wars: TIE fighter (1994), though, Thrawn holds the rank of Vice Admiral at the beginning of 3ABY. So… was he in fact a Vice Admiral in 2ABY in Command Decision? Or did he get demoted? Knowing the guy, it wouldn’t surprise me… XD
This part is much trickier to make sense of. Technically, the most recent source of information here is Side Trip, but Thrawn being a Grand Admiral in 2ABY contraddicts too many other sources and doesn't line up with the chronology. I personally think that the Fleet Admiral hypothesis is the one that makes the most sense.
He most likely was a Vice Admiral at some point... certainly not after 2ABY, and a jump from Senior Captain to Fleet Admiral is unlikely even for Thrawn.
In late 2BBY Thrawn is called back to Imperial space again to deal with pirates in the Pakuuni system. We do know that this time he leaves the Admonitor in the Unknown Regions as in the campaign against the pirates Thrawn’s flagship is the Victory-I Star Destroyer Stalwart.
During this brief period he spends in Imperial space he also moves his flag quite frequently from VSD Stalwart to ISD Vanguard and to VSD Sceltor during the early stages of the Zaarin campaign until he seemingly settles down with ISD Grey Wolf: that is the ship he journeys to Coruscant on to receive his promotion to Grand Admiral.
Grand Admiral
We know from Dark Force Rising (Timothy Zahn, 1992) that he gets appointed to Grand Admiral on Coruscant in a very private ceremony:
«“All right, then,” Mara said. “We met once, during the public dedication of the new Assemblage wing of the Imperial Palace on Coruscant. At that ceremony the Emperor introduced me to you as Lianna, one of his favorite dancers. Later, during the more private ceremony that followed, he revealed to you my true identity.” “And what was that private ceremony?” “Your secret promotion to the rank of Grand Admiral.”»
Palpatine promotes Thrawn to Grand Admiral from Star Wars: TIE Fighters
Star Wars: TIE fighters tells us he gets the promotion thanks to his merits in the Zaarin campaign and that Palpatine’s intention had always been to replace Grand Admiral Zaarin with the Chiss since the very beginning. I wonder, though, if the victory at Derra IV played some role in the promotion as well: despite being Thrawn the mastermind behind the strategy that brought Imperial forces to triumph, Soontir Fel in X-Wing Rogue Squadron #25 says everyone got a promotion after the battle except Thrawn. Didn’t he though?
We also know from Star Wars: TIE fighter that he was promoted Grand Admiral around 3.5ABY, and the Battle of Derra IV took place halfway through 3ABY… timing lines up.
After the promotion ceremony, Thrawn heads back to the unknown Regions where he continues his "mapping" mission and deals with local warlords such as Nuso Esva who he first clashed with in 2ABY when he was still just a Senior Captain.
The Admonitor remains his flagship until 8ABY when he transfers his flag to Cpt. Pellaeon's ISD Chimaera, and sends the Admonitor back to the Empire of the Hand under the command of Cpt. Niriz and Cpt. Voss Parck. It is worth to be noted that none of the two ships of the Admonitor Task Force we know the name of, the Admonitor and the Iron Fist, joined Thrawn in his campaign in 8-9ABY.
In fact, we know that Thrawn travels alone to meet with Pellaeon on the Chimaera leaving the Empire of the Hand to deal with the remnants of Nuso Esva's forces.
«“I hope not.” Parck took a deep breath. He still didn’t like this, but he knew better than to argue when Thrawn’s mind was made up. “With your permission, Admiral, I’ll go begin preparations to contact Captain Pellaeon and return you to the Empire.” He smiled slightly. “To your Empire.”» Crisis of Faith, Timothy Zahn, 2011
Thus none of the six Star Destroyers that make up Thrawn's personal armada in his campaign for the restoration of the Empire (namely the Chimaera, the Death's Head, the Inexorable, the Stormhawk, the Judicator and the Nemesis) is part of the original Admonitor Task Force.
In conclusion
Despite being said that he rose through Imperial ranks very quickly, Thrawn's career really got a boost in his last years of Imperial service going from Senior Captain to Grand Admiral in less than four years.
From 1BBY to 8ABY, he had under his direct command 7 capital ships (ISD Vengeance, VSD Iron Fist, ISD Admonitor, VSD Stalwart, ISD Vanguard, VSD Sceltor, ISD Grey Wolf), with the ISD Admonitor being his main flagship as she held the status for six years.
It is also curious to notice that his naval career only started in 6BBY with the rank of Senior Captain, while it is unsure to what kind of Navy corp he belonged to previously. It is fair to assumed he was somewhat linked to Starfighter Corps as the rank of Colonel suggests.
It is also worth remembering that he always was some kind of a wild card, most of the time acting outside common Navy regulations, carrying out very specific and secret mission for the Emperor himself and holding a far greater influence in the Imperial politics than he let out.
Be mindful this scheme, though as accurate as possibile, is necessarily been subjected to a certain degree of approximation... makes the idea though ^^. (EDIT: I decided to align the rank of Senior Captain with the beginning of the Kaleesh-Imperial conflict, though we don't exactly at what point between 6 and 1BBY Thrawn actually achieved the rank).
Let me know please if I missed or misinterpreted something, I'd love to start a healthy debate :)