M0
From X3 Wiki
M0 Mothership
M0 are the heaviest ship class and, prior to the Terran Conflict, were used only by Xenon and Kha'ak. They are used as a story element, where their purpose is to destroy planets - or rather to be stopped from doing that by the player.
The Xenon M0 appeared in X: Beyond the Frontier. In X3, its remains can be found in Xenon Sector 101.
The Kha'ak M0 appeared in X2 in the battle for Omicron Lyrae.
In Albion Prelude, the ATF Valhalla is, canonically, an M0 Mothership, combining the firepower of a M2+ destroyer with the force projection of a massive carrier.
Note[edit]
It should be pointed out that in X3: Reunion and X3: Terran Conflict no actual M0 classification exists in the game files.