I had heard, years ago, of a plan to try and salvage a car that was in the cargo hold of SS Andria Doria. The salvagers said that the conditions (depth, temperature) made it likely that the car hadn’t rusted at all.
However a quick check of the wikipedia entry show the ship itself has not fared well, so that idea for how a ship might remain in decent shape underwater for 30 years appears dead.
For an interesting way to raise a sunken vessel, try filling it with ping pong balls. Mythbusters have shown it can work. I first heard of this in a story that a guy wanted a patent on the process, and was denied because the relevant authority had remembered seeing it in an old Donald Duck comic.
Construction had begun on Kentucky, at least. When USS Wisconsin collided with a destroyer in 1956, the repair was expedited by taking a 68 foot section of Kentucky’s bow and using it to replace Wisconsin’s damaged bow.
Because the transplant didn’t match perfectly, Wisconsin is actually longer than her sisters by 16 feet.
I think a scenario where the ship is retired to some other role - like floating oil jetty is a more useful option.
Maybe you can use HMS Warrior or SS Great Britain as an idea.
Both ships were retired, partly stripped down and their history largely forgotten, and then they were rediscovered and restored.
You could imagine an Iowa class battleship being moored up and pretty much forgotten and left largely intact or even was used as a floating test platform for some new weapon control system - this has changed her profile significantly so she does not have the romantic old lines, then imagine its a sister ship to one that is much more famous that is being used as a floating museum. That is why she gets forgotten.
Your forgotten Iowa class battleship has some new technology but is deemed as out of date with its huge guns(perhaps even militarily unfashionable), however its the very combination of those guns and the super control system that makes her the only vessel in the world that is capable of your mission.
That they were. There was a lot of editing done from Space Battleship Yamato to Starblazers we were too young to catch on to. The doctor wasn’t ‘happy’ all the time and drinking ‘spring water’, he was constantly drunk on sake. The sexual content is removed, a good part of the WWII references are removed (including the entire scene in episode 2 of the Yamato being sunk by American aircraft while on its suicide mission to Okinawa) and the ship is renamed the Argo in Starblazers, the significance of Yamato being lost on an audience of American children; Yamato refers to the entire Japanese people as a race.
Though the magazine explosion as the Yamato sank makes the far fetched idea of turning it into a space battleship even more implausible.
