The Imperial Knights Lost Fleet was a fleet formed by Knight-Commander Bellatrix La Rouge during the Third Galactic Civil War. Originally amassed to serve as the naval force of the Imperial Knights-in-exile, with the Excalibur as its flagship, Rouge hid the entire fleet in an unknown location only known as Siege-1. Only Rouge, Ayumi Pallopides, and Commodore Barrel knew the location of Siege-1. With Rouge killed by Darth Illusia, and Operation Twilight killing Pallopides at HOMEFRONT and killing Barrel aboard Excalibur, the location was lost to the Imperial Knights. However, Rouge left clues with her son, K. Together with Athos, K and Athos sought out the missing fleet.
The fleet was comprised of Fisher King, Marked King, Lady's Lake, Ashla Emperor, Rouge's Knight, Green Knight, Beast Quest, Round Knight, Pen Dragon, On-Rhea's Brand, Goodwood, Savage Oppression, and Trak Nar. Excalibur and Harrowing are considered a part of the fleet, but were not stored at Siege-1 and were destroyed during Operation Twilight.
Behind the scenes
[Y]ou'll probably notice a lot are homages to Arthurian stuff.
—Dmitri Valentine to "Shiuzu", Athos' creator from TheStarWarsRP.Com
The Imperial Knights Lost Fleet was created originally as a normal stored fleet at a undisclosed location as a part of a plot during the fifth timeline of TheStarWarsRP.Com. However, with the death of Bellatrix La Rouge and the other two confidants led to the fleet to be unreachable.
During the naming of the ships, creator Dmitri Valentine made many homages to individuals from Arthurian legend, which some other Imperial Knights have been themed after. For the remaining ships, they were named after administrators of Star Wars Fanon. The largest ship, Round Knight, was cataloged as a Troop Carrier Type-999, or TC-999 for short, a homage to administrator TK-999.