SUMMARY
The Battle of Sargasso was a conflict between invading Covenant and defending UNSC forces on the colony of Sargasso on September 21st, 2546. During the battle, ODST squad Alpha-Nine, led by Edward Buck was sent to recover important military research data from a weapons manufacturing facility on the colony. Alpha-Nine successfully recovered the data, and was able to rescue Sarah Palmer, the last remaining survivor of Gamma-Six squad, during their extraction.
The outcome of the battle is not known, though it was likely a UNSC victory, due the Navy's ability to fend off the Covenant fleet.
RELATED MEDIA
These events are depicted in the novel Halo: New Blood, which was the subject of a Halo Book Club episode on April 28th, 2015.