From Halopedia, the Halo wiki
Blue Six was a unit present during the Second Battle of Harvest. They were an outfit of four M12 LRV Warthogs and two modified turretless Warthogs. The outfit was seen leaping over a rise in a snowy night landscape on Harvest. Two Marines from the outfit radioed in to the UNSC Spirit of Fire to confirm they were joining with Blue Five, an outfit consisting of five M808B Scorpion tanks. Both units then headed towards the last known position of a recon force with whom communications were severed. The recon patrol was then able to radio back to Blue Six, explaining they were under attack. A member of Blue Six then listened over the radio as last member of the Recon patrol was killed by an Elite with an Energy Sword.