The 4th Fleet was an old task force created during the Koslovic crissis, during the formation of the UNSC it becaume the UNSC 4th Fleet. This fleet participated in 35 battles during the great war. It was put in charge of protecting mars in the early 2550's and was refited with Halycon Class Cruisers. After failling to protect mars 4th Fleet was ordered to form a task force with Earth's home fleet in order to halt any offensive Covenant maneuvers in and around Earth orbit.