The Primus Redoubt is what happens when you want to mount a Titan gun on top of a Bunker. Because fuck you that's why!
The Primus Redoubt is a super-heavy emplacement usually built by the Imperium to defend vital locations such as cities or foundries. Protected by its heavy walls and a force dome, the Primus Redoubt can withstand practically anything thrown at it.
According to the fluff, they can be armed with a variety of heavy weapons that are more usually found on void ships, powered by a generator deep beneath the main emplacement structure. Yet crunchwise it carries a twined Turbo-Laser Destructor. Not weak by any means...but still far below the level of main weapons on an Imperial voidship.
Hilariously mislabelled Primaris in the Index. This fortification takes up a Realm of Battle tile to deploy and has a massive titan-strength fuck-off laser. It enjoys being able to actually hit with the thing with BS 4+. Nowhere near as tough as it once was, but also much cheaper in points. At less than a third the cost of a Warhound, it's not a bad way to get a cheap(ish) turbo-laser. It can't really be spammed, though, what with it being a RoB tile.