From Halopedia, the Halo wiki
In 2558, during the attack on the UNSC Infinity, Lancer was ordered to reinforce Fireteam Avalanche and Fireteam Kodiak at Fore Armory 12-7. After securing the armory, Lancer was sent to Translight Deck 19-7 to reinforce Fireteam Crimson. Later, after Crimson secured "Apex," Lancer was sent in to guard the area.
While protecting the Apex, Lancer discovered a Covenant base in the nearby hills. Commander Sarah Palmer ordered Crimson to assist Lancer in destroying the base. Crimson regrouped with Lancer and together the two fireteams destroyed the shield wall protecting the generator. Lancer and Crimson made their way through the canyon and reached the entrance to the Covenant base. While the two fireteams were attacking the base, Jared Miller picked up a mysterious SOS signal, originating from a nearby cave. Lancer and Crimson made their way into the cave and discovered the captured Fireteam Switchback. Shortly thereafter, the Crimson and Switchback were evacuated.
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