Titan vessels...such a bounty of lore that should follow one.
Let's see:
This splendid leviathan was the first, and last, lead ship for the Persean League Navy's proposed intergalactic colony expedition. A single hyper-wealthy donor poured his entire dynastic family fortune into this single ship with the stated purpose of ensuring that his organic body (in cryo) would arrive in the next galaxy intact. Her reactor core features a single cryo couch buried within a 10 meter cube of battle steel.
The idea was to field an unstoppable mobile base that could fund itself while the rest of the expedition was being built. Unfortunately, new hostilities broke out before the security on the project could be upgraded, and the Hegemony acquired a basic schematic of the design. The Hegemony baited the Athena task group into committing to extended range, fruitless deployments long enough for the operating and personnel costs to force the ship to be idled.
The choice of where the ship was idled, and who made that decision, is a source of endless discussion. Less then two days after the ship arrived in orbit of the inactive gate...the ship then disappeared, likely through the gate. How the gate was reactivated, and only once, is unknown.
Indeed the location of the ship itself, is currently unknown. Why exactly someone would go through the trouble of acquiring a single vessel capable of standing off a Grand Fleet of Syndria, then do precisely nothing with it, is also unknown. Coincidentally, the hyper-wealthy donor also disappeared at around the same time period.
Fleet planners generally consider the possibility of a reappearance of the Athena to be outside the realm of realistic planning. The public at large, and especially military science fiction literature, see the Athena as the the mystical ghost ship of fate. The Sword Excalibur waiting to be discovered and used to solve The Big Problem with titanic, overmastering salvos.