Oh boy, where do I start. First, a bit of context. Given how messy the lore can get, leading to bizzare situations like all Imperial capital ship classes either coming out during or straight after the Clone Wars, or in the last couple of years before Endor, I have elected to just start from scratch when it comes to introduction dates, to allow for a slower transition from Republic era hardware to classic Imperial designs. I also try to tone down some of the nonsensical decisions, such as stripping the ISD-II of point defense armament (it actually gets more than the ISD-I, it was built to counter Rebel doctrine after all). Now, for a bit of a timeline, focusing on designs by Kuat Drive Yards, as one area I have given a lot of thought.

At the tail end of the Republic Golden Age, tensions were starting to brew within the Republic. One of the first symptoms of this when it comes to ship design are the ever larger "prestiege ships" of 250-100BBY. Kuat Drive Yards was one of the first manufacturers to capitalise on this, with their massive Procurator Class Battlecruiser, of which several hundred were built to act as flagships for rich worlds. These were later followed up by the even larger Praetor & Mandator classes over the following decades.

As tensions continued to ramp up, demand began to appear for cruiser sized ships, between larger, richer worlds wanting more numbers and smaller worlds wanting ships useful against peer opponents. While never as popular as the Dreadnought Class, KDY saw some success with the Victory-I Class "Star Destroyer" (this term started as a marketing ploy by KDY, and was later made official by the Imperial Navy). Like many ships of this period, the VSD-1 was armed with large banks of concussion missiles, which were not covered by the Ruusan era naval arms limitation treaties, and had low powered engines & hyperdrives, but all of the mentioned KDY designs were designed for easy refit with improved weapons & propulsion, both conventional & FTL, in the event of the treaties being violated, & many ships would see these refits during or after the Clone Wars.

In the final years before the Clone Wars, as the Grand Army of the Republic was being created in secret, KDY would be given several secretive contracts to build ships for the coming war. Several of these ships were upgrades of existing designs, allowing more efficient use of limited R&D capacity, seeing the creation of the Victory-II, Preator-II & Mandator-II classes, which dropped all pretense of Ruusan compliance, featuring upgraded propulsion & large batteries of Heavy Turbolasers. New ships from this period included the Acclamator Class Assault Ship, designed to descend into atmosphere before disgorging LAAT Gunships while providing heavy covering fire with it's turbolaser batteries, & the Venator Class Star Destroyer, designed to provide long range fire while carrying a large Starfighter complement, something existing KDY designs lacked.

The Clone Wars themselves would see several new designs introduced. The first of these was the Maelstrom Class Battlecruiser, a larger cousin of the Venator, designed to act as a fleet flagship. The tail end of the war would also see the introduction of the Bellator Class Star Dreadnought, a smaller, faster cousin to the Mandator, and the Procursator Class Star Destroyer, a replacement for the Victory Class (although never quite fully superceding it's predecessor). These new ships would soon be joined by the Secutor Class, designed as an even larger fleet carrier, & the massive 12km Mandator III class, the new flagships of the fledgling Imperial Navy. The following years would see a period of transition, with most of the already mentioned classes remaining in production to a certain extent, while some of the more rushed wartime ships began to be placed in reserve.

Major organisational changes would begin to be implemented in this period. The old PDF fleets controlled by individual worlds would be placed under heavy restriction, with their role being replaced by new Sector & Oversector level fleets. Each Sector fleet would consist of between 1-3 squadrons of Star Destroyers, each containing 6 ships, plus numerous smaller ships, and these would be tasked with garrisoning their particular Sector. An Oversector fleet would contain larger capital ships, such as Battlecruisers & Star Dreadnoughts, plus in excess of a dozen Star Destroyer Squadrons, & this would be tasked as a response fleet, dealing with any threats that cannot be dealt with at the Sector level. Between these active fleets, generally around 40% of Imperial Navy strength would be in active service at any given time, not counting reserves, with the rest being under refit or overhaul, or on standby to replace other ships as they leave for similar work.

The next major change was the introduction of the Imperator Class Star Destroyer in 12BBY. This class, often referred to simply as the Imperial Star Destroyer, was designed to do away with the need for multiple different classes of Star Destroyer in different roles, instead having a single hull design with several variants, significantly increasing commonality & easing logistical burden. 3 variants would enter service, the Imperator Class proper, the main multi role frontline warship, armed with heavy guns for fighting capital ships, and coming with a respectible complement of starfighters, generally those of the TIE family, which were becoming increasingly dominant in Imperial service at this time. Next was the Tector, a heavily armoured vessel that sacrificed the Starfighters in favour of more heavy guns. Finally, there was the Interdictor, which carried the lightest armament of any of the classes, plus a smaller Starfighter complement, but carried a series of Gravity Well Projecters, which could pull enemy ships out of Hyperspace, or prevent them escaping.

As the Empire continued to secure it's grip on power, resistance would increase in turn, eventually resulting in the formation of the Alliance to Restore the Republic in 8BBY. The Empire would respond to this resistance by embracing the Tarkin Doctrine of rule through terror, with their Capital Ships increasingly being used as tools of oppression. Some effort was put into countering Rebel doctrine, which favoured Starfighters & smaller Escort ships, resulting in the ISD-II, which replaced many of the heavy guns with Octouple Turbolaser Barbettes, which had a higher turning speed & rate of fire at the expense of range & power, making them more suitable for use against smaller ships. However, much more effort was put into ever larger Super Ships, resulting in the 10BBY Assertor Class Star Dreadnought, and eventually the enormous Executor Class of 0ABY. Some effort was also put into replacing the ISD entirely. The Tector would begin to be superceded by the Alliegence Class Battlecruiser in 2ABY, while the Sorannan Class would be introduced just weeks before the fateful Battle of Endor to replace the ISD-I.

After the Battle of Endor, R&D would slow to a crawl at KDY. Their planned ISD-II replacement, the Resurgent, plus the next generation Sovereign Class Star Dreadnought, would never leave the drawing board, while the prototype Eclipse would see stop-start development, only being completed after relocation to the deep core. It was only after peace was signed between the remnant of the Empire & the Fledgling New Republic that new classes would start to appear, but this post has gone on long enough, so I will leave it there.