The Death Star was planned and created in between Episode III and IV of the saga.
This question deals with the creation of Star Destroyers in general: In what year did the first Imperial-class Star Destroyers enter service?
My question is: when did the design and creation of the Executor class star destroyers take place, and how many did the Empire build?
When they were designed is unknown. Since they’re not considered superweapons like the Death Star, they didn’t get their own book detailing their design. There’s some evidence that they may have been in the pipeline as early as 11 years before the Battle of Yavin:
“The thorilide triangle,” Skelly said, astonished that she hadn’t heard about it. He moved across the room to the other side, with his wall of corporate shame. “The mining firms are corrupt. They’re tied up—ownership, boards of directors—with the shipwrights that have sold the Empire on one construction project after another. Oh, it’s all being done in secret, but you can’t keep everything secret. A billion Star Destroyers isn’t enough. They’re building Super Star Destroyers, and Super Super Star Destroyers, and who knows what else!”
A New Dawn
Though this information comes from an unbalanced conspiracy theorist, his use of the term Super Star Destroyer seems a little too coincidental, and he was right about some other things.
They were almost certainly built and deployed, though, between A New Hope and The Empire Strikes Back, since they didn’t appear in A New Hope or Rogue One, but they did participate in the Battle of Hoth.
As for numbers, we do know that there were thirteen Executor-class dreadnoughts (a.k.a. Super Star Destroyers) in existence before the second Death Star was destroyed.
She starts with the Dreadnoughts—the Super Star Destroyers.
Thirteen were in service before the revivified Death Star was destroyed above Endor. One of those is the Ravager, the SSD from which Sloane rules the Empire (and which, strictly speaking, is now Gaelan’s command). One of those is the Executor, Vader’s command ship. The Executor was lost that day, plunging into the surface of the Death Star. Taking hundreds of thousands of the best Imperials with it.
While we can’t rule out the possibility that the Rebellion destroyed some before the Battle of Endor, or that some might have been lost to other events or actors, it seems likely that they weren’t, and so thirteen is probably the number of Executor-class dreadnoughts that were built.
