The earliest mention of COALMINER was in 2532, where a message to Codename: SURGEON concerning the S-IIIs, COALMINER noted the early stages of preparing Alpha Company were progressing satisfactorily and expressed confidence in Kurt-051's training regimen.
In 2552, COALMINER detected an intrusion into the ONI database at Reach. While COALMINER failed to identify the intruder, the intrusion threatened to compromise HYPODERMIC. COALMINER informed SURGEON of the breach and deleted the UNSC Circumference from Reach Station Gamma's database to minimize the damage.
This later caused difficulties during the Fall of Reach as it prevented the AI Doppler from erasing the Circumference's NAV database as per the Cole Protocol. A SPARTAN-II team had to deploy to destroy the ship and suffered casualties in the process. This may, however have effectively saved John-117 and humanity, as John-117 may have died or been trapped on the planet, and would not have taken part in the destruction of Installation 04. This may have also saved the lives of many other notable characters, such as Sergeant Johnson and Cortana.
After the war COALMINER was given reports on the Post-war state of the galaxy from SURGEON.