From Halopedia, the Halo wiki
During the Battle of Sigma Octanus IV on July 18, 2552, Cochran and his squad encountered Hunter units, and retreated. During the following escape, he was wounded by a Covenant Grunt's Needler. Harland was able to patch the wound up with biofoam to keep him alive until he could get medical attention. Despite being wounded to the verge of death, Cochran managed to take the rocket launcher from Private Walker, who was in a state of shock and could not do so himself. Cochran shot down the Banshees and saved his squad.
With the help of Spartan-117 and the other SPARTAN-IIs, the fight on Sigma Octanus IV was a success and Cochran lived to get medical attention, though he slipped into a coma after arriving at Alpha Base.
Cochran does not appear in the comic adaptation, Halo: Fall of Reach. Instead, Walker is able to regain his faculties and shoot down a single, lone Banshee.
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