From Halopedia, the Halo wiki
The UNSC Coenwulf was a vessel in the UNSC Navy. After the Battle of Sigma Octanus IV on July 17, 2552, Vice Admiral Michael Stanforth requested that the crew of his flagship, the Leviathan, be transferred to the Coenwulf, as the Leviathan required at least two months of repair work. Meanwhile, Stanforth would "make rounds" in Sydney, Australia on Earth, presumably at HIGHCOM Facility Bravo-6.
The vessel is named after Coenwulf, the king of Mercia between 796 and 821 CE.