From Halopedia, the Halo wiki
During the Flood Outbreak of Installation 00, the Banished Jiralhanae Warlord Pavium operated a trio of these salvage drills near a Forerunner defense station which contained the Archive. Pavium used the salvage drills to destabilize the chemicals in the ground underneath and destroyed the Flood growth at the entrance to the Forerunner defense station. The destruction of the Flood growth allowed his brother Voridus to enter the facility and reactivate the Forerunner defense network to combat the flood.
Three salvage drills appear in the Halo Wars 2 DLC Awakening the Nightmare, during the campaign level Light the Fuse, in which the salvage drills serve as the level's main objective. The salvage drills also appear in Skirmish map Fissures, which uses the same level geometry as Light the Fuse, but players cannot interact with the drills .
Players need to destroy crystals found throughout the map to collect Power to activate the drills. Each drill requires 8,000 Powers, so a total of 24,000 Power is required. Upon the drills' activation, the Flood will attack the drills to deter the player's progress. The mission ends in failure the drills are destroyed.
Concept art of the salvage drill had depicted the machinery as the "Banished Mining Rig". It also shows the rig over multiple stages of construction, suggesting players were originally tasked with constructing the rig rather than collecting Power to activate it. The design was carried over to the art for the Skirmish map Fissures.