You are referring to either the Praetorian or the Interrex. Both have four variants you can choose from and they are pretty good, so I'll not delve into details.
Praetorian is like a cross between the Hammerhead and the Enforcer. Slow and tough like the latter, but damn shooty like the former. Its rear defences are abysmal, though, so you have to prevent that from happening by having escorts. It's supposed to mainly hold, like Enforcer, but with a fair bit more firepower. While it's possible, I wouldn't use its medium turret for point defence, except for the Sagittarius.
Interrex is more about flanking striking, helped by its mobility ship system and better missile capability. It has even worse rear defences, but it should be mobile enough to get out of the harm's way before that happens. It doesn't have the slots to spare, but it has a decent shield.