I was just reminded of the Tector-class Star Destroyer, and how weird it is, by the excellent YouTube channel EckhartsLadder in this video. I shall quickly place this odd ship in context. The Tector is an Imperial II-class (or Imperator II-class, if you prefer) Star Destroyer variant seen in one shot of Return of the Jedi, and its main distinguishing feature is that it only has a very small ventral hangar bay rather than one capable of containing Princess Leia's corvette. It also seemingly lacks the typical aftward bulb-like protrusion you see on most Star Destroyers.
Star Destroyers typically fulfil a battle-carrier role akin to that of the Battlestar Galactica in the eponymous franchise; they are heavily armed and armoured, and have a considerable fighter wing. Star Destroyers have retrospectively become a very poor design choice. This is due to a number of factors.
First, George Lucas did not really think his universe through, and wanted more shiny toys in the Prequels. This led to the odd situation where it's perfectly clear that a single Venator-class Star Destroyer (one of the earlier and weaker ships seen in Revenge of the Sith) carries a large enough fighter wing to overwhelm the defences of a Star Destroyer in the later period. I'd like to note at this point that if you give anyone effectively unlimited funding and carte blanche in their creations, you should not be surprised if things go awry.
Second, game designers and authors followed up on part of what we see in the films, giving players and readers the opportunity to participate in the plucky little fighters attacking these "city-sized" warships. Again, this is perfectly understandable.
However, as I said above, what we end up with is a situation where the notionally more advanced later ships are very much worse than the older ones. A swarm of small fighters can take out one of these large battlewagons in a prolonged fight because the larger ship possesses neither the point defence capability of older, smaller models, nor their fighter capacity, while the swarm carries a number of missile weapons capable of knocking down the target's shields and destroying it. Neither the ship's armour, nor its shields are capable of resisting this swarm attack. The vessels' ability to carry about 10,000 troops does not justify this odd situation. Truly, Star Destroyers have retrospectively becomes jacks of all trades, and masters of none.
There is the context. Into this milieu the Tector-class Star Destroyer is introduced. The ship lacks the aftward ventral bulb that distinguishes the Imperial and Imperial II classes. It's reasonable to infer that this means that she is more heavily armoured. The ship's reactor (which is what the bulb is) is more heavily protected in the ship's innards. The vessel also lacks significant ventral hangar bays, and other sources have clarified that this is not made up for by the provision of replacement hangar bays dorsally or on either flank. I'm not even sure, from what we see, that the ship is capable of launching or receiving Lambda-class shuttles. I am happy to be corrected.
The ship lacks the fighter protection enjoyed by its close relatives, sacrificing it for armour and shileding that, we have established, are not sturdy defences in-universe. Moreover, it sacrifices another of the Star Destroyer's typical roles: planetary invasion or the ability to put boots on the ground. Without a large hangar, there is no way to launch the mammoth four-legged AT-ATs, the companion two-legged AT-STs or "chicken walkers", or even large contingents of infantry.
The ship lacks the fighter protection enjoyed by its close relatives, sacrificing it for armour and shileding that, we have established, are not sturdy defences in-universe. Moreover, it sacrifices another of the Star Destroyer's typical roles: planetary invasion or the ability to put boots on the ground. Without a large hangar, there is no way to launch the mammoth four-legged AT-ATs, the companion two-legged AT-STs or "chicken walkers", or even large contingents of infantry.
What is this thing for? Typical Star Destroyers of the I-line have a crew of c.37,000 and pack in another 10,000 soldiers. I'm going with the figures of my youth, so bear with me if the canon has changed. I was surprised earlier to see that Interdictor-class cruisers are now 900 metres in length. They were 600 once. Anyway, this ship certainly doesn't need that many Stormtroopers and vehicles if it can't get them out. The sources suggest that this design of vessel superseded the Venator because it was sturdier, which is a terrible argument. It is more specialised for capital ship combat, ignoring the vital fighter element, and is incapable of effecting a planetary invasion.
My best justification for this ship is that it is a taskforce or fleet flagship. Extracting ten thousand men lets you put in all sorts of communications goodies, and with the additional armour, the ship can survive longer in combat, decreasing command and control problems. Frankly, that's not a great justification. It's a Star Destroyer, so it's already very difficult to destroy, and in a ship that's a mile long, you can probably find a couple of rooms to jam in all the personnel you need to coordinate a fleet.
That's the Tector-class, folks. It's a ship that doesn't really make sense in a place where ships don't really make sense. Perhaps surprisingly, given how exactingly I've taken it to task for its deficiencies, I rather like it!
Links:
http://starwars.wikia.com/wiki/Tector-class_Star_Destroyer
http://starwars.wikia.com/wiki/Tector-class_Star_Destroyer/Legends