Battle of Ballast
From Halopedia, the Halo wiki
The Battle of Ballast was a battle that took place on the UNSC colony of Ballast during the Human-Covenant War. It is unclear if the UNSC or Covenant forces on the planet won the battle, but propaganda produced by ONI stated that the battle was a UNSC victory. Signs on the Quito Space Tether hint that the colony still existed during the Battle for Earth.
The marine battalion E2-BAG/1/7 was involved in the battle and afterwards provided feedback on munitions used as part of a study entitled Machines, Materiel and Munitions from the Human-Covenant Conflict, 2525 - Present.