SUMMARY
The Battle of Leonis Minoris was a battle between Covenant and UNSC forces in the Leonis Minoris system sometime in 2537. The battle eventually resulted in a UNSC victory after Vice Admiral Preston Cole and his fleet entered the system to protect the three colony worlds there, but not before the Covenant were able to glass two of the colonies and destroy ten of the fleet's ships.
RELATED MEDIA
These events are referenced in the short story The Impossible Life and Possible Death of Preston J. Cole, in the anthology Halo: Evolutions, which was the subject of a Halo Book Club on January 3rd, 2018.