Naval Captains = O6 pay grade ((equal to a Colonel in the ground force ranks). This does not seem to used in SWU.
Captain Piett, Captain Needa, Captain Pellaeon...
"Captain" Solo wasn't commissioned in the Rebel Fleet prior to ROTJ
Iffy. In ESB, he wore the same brown-with-yellow trousers Luke wore at the end of ANH. Some people say Luke was given a pair of Solo's pants for the ceremony. This always struck me as ridiculous, as Mark was nearly a foot shorter than Harrison. I thought it was perfectly clear that Luke joined the Alliance as soon as Leia vouched for him and they set about getting him a flight suit and uniform. There's a whole lot of other speculation from over the years that the Prequels really messed up, that made more sense than what we ended up with now, like that the uniforms worn by the Alliance were Republic uniforms, the flight helmet decos Republic Navy squadron markings, etc. This was the Alliance to Restore the Republic, and the Empire was a fairly recent thing...
...So a lot of us in the fandom in the early days of the internet, talking about it in AOL chat rooms, on useNET, at conventions... We figured what Luke was wearing at the end of ANH was the old duty uniform of a Republic Navy starfighter pilot, the Dagobah/Bespin outfit an undress/fatigue uniform, and that Han wearing the same pants in ESB indicated he'd joined the Alliance -- but his insisting on wearing his own shirts and jackets was his refusal to give up his independence
altogether. But his rank is unknown. General Rieekan only ever addresses him as "Solo". Vader and Fett both refer to him as Captain Solo, but that seems to be based on their knowledge of him as the owner and operator of the
Falcon. I doubt the Alliance makes public postings of their promotions schedules.
So despite what the Prequels would later do to the context of things in the OT, I feel the intent of those pants was to show he was more part of the Rebellion than he was the last time we saw him. How much is not clarified. He has to have more clout than a civilian to be ordering around the Echo Base personnel as he was doing, but he addresses Rieekan as "General", implying (to me) a sense of subordinance. Maybe a Colonel? Since it's the Air Force equivalent of a naval Captain, and armed freighters occupy an air-force-y position in the Alliance fleet, from what both the
Falcon and the
Ghost are shown to be doing.
My way of justifying his "sudden" General-ness in ROTJ over the years.
But, if you'll forgive the term, in general they seem to use that rank fairly consistently in Star Wars. Remembering there are multiple tiers of the rank. Definitely much more sensically than "Commander". Oy.
--Jonah