Bucephelus

The Bucephelus was a golden Battle Barge or Battleship of unknown class that served as the personal flagship of the Emperor during part of the Great Crusade. The Bucephelus maintained a garrison of Legio Custodes and took part in the titanic Battle of Gyros-Thravian when the Emperor was forced to deploy the Custodians to reinforce the Space Marines of the Imperial Fists, Luna Wolves and Death Guard Legions in their battle against the Orks of Warboss Gharkul Blackfang. At some time during the Great Crusade, the Emperor moved His flag to the Imperator Somnium.

Trivia
Bucephalus was the name given to the beloved warhorse of Alexander the Great.