Marathon-class Cruiser
From Halopedia, the Halo wiki
The Marathon-class Cruisers are some of the most powerful warships in the UNSC fleet. They were the replacement for the aging Halycon-class Cruiser. However, due to their diminishing numbers, furhter numbers of these great vessels have been retrograded to the Inner Colonies.
These behemoths, clocking in at 1192 meters, approximately two and a half times the length of a UNSC Frigate, sport at least three Magnetic Accelerator Cannons (according to an outline of the Marathon classification), probably amongst other armaments. They are also known for their heavy armor - they can survive multiple plasma torpedo impacts, far greater damage than any UNSC Frigate or UNSC Destroyer can sustain.
Marathon-class cruisers were seen at the Battle of Sigma Octanus IV, the Battle of Reach, the First Battle of Earth. Eight or more Marathon-class cruisers battled in the First Battle of Earth under the command of Fleet Admiral Harper. It is very likely that these cruisers also participated in the Second Battle of Earth.
