This is similar to the Homeworld2 backstory - the third of the three Hyperspace Cores has been found by a militaristic nomadic race called the Vaygr, and their leader Makaan is conquering system after system. (
WARNING: If you read on you will get a major spoiler!)
The Mothership and its fleet fights off several Vaygr attacks before they find a device called the "Oracle" which is apparently an ancient "Progenitor" device, made by the people of Sajuuk. The Oracle takes over the Hyperspace core and takes the mothership to the wreckage of an unbelievably huge Progenitor ship (you see a film where the Mothership, being 2.5km in height, is shown in comparison to the Progenitor ship. My first reaction was "OMFG that thing is HUGE!") where you must find an ancient super-warship - a Dreadnaught (no, this is spelled correctly) - called the "Gatekeeper of Sajuuk". You discover that the Progenitors were an extra-galactical race (Ocampa Caretaker, anyone?) and that their relics aren't as passive as you might think (or want). They've still got AI controlled warships, Movers, Drones and most notably Keepers, who are undestroyable uber-warships. At first you (both as a Hiigaran and as a player) think the Dreadnaught will give you superior firepower and that you will win easily, but it turns out there is a second Dreadnaught in the posession of the Vaygr. I have not yet reached the point where I encounter it, but it was said in a cutscene movie. I am currently at mission 12 of 15, Thaddis Sabbah. Any tactical advice would be appreciated
