From Halopedia, the Halo wiki
During the Fall of Reach, Buckman shared command of Charlie Company with First Lieutenant Jake Chapman, commanding the sub-unit Gamma 5. On August 30, Buckman and Chapman ordered a carpet bombing by numerous Longswords to eliminate the Covenant forces attacking ODG A-331. The attack was poorly targeted, leaving a large part of the company dead. After the incident, only four members remained at Generator A-331, while Buckman and parts of Gamma 5 proceeded to defend ODG A-412.
After A-412 was overrun as well, Buckman and Gamma 5 regrouped with Gamma 1. Beta Red bought them some time by stalling a massive Covenant ground force. Buckman and Gamma 5, along with Chapman and Gamma 1, retreated and headed for a temporary evac station. Just then, three Covenant cruisers appeared over them, headed towards Beta Red's position. The UNSC Majestic was called in to perform a MAC strike on the cruisers, despite Beta Red, Gamma 1 and Gamma 5 being in the splash zone. Though the status of the rest of their units is unknown, Chapman and Buckman survived the blast.
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