From Halopedia, the Halo wiki
UNSC Bucephalus is an Eclipse-class prowler. It was also the mothership to the Owl the UNSC Special Delivery.
On October 6, 2559, the UNSC Bucephalus conducted a threat sweep of the human colony world of Reach. This was done in preparation Blue Team's Operation: WOLFE. The sweep detected a low intensity conflict and radio chatter but it's intruments weren't sensitive enough to determine details of the battle.
Bucephalus was the horse used by Alexander the Great.