Fifteen years prior to the Battle itself, the IMC flagship IMS Odyssey would undergo a mutiny in which James MacAllan would emerge victorious. The ship would crash-land on the unexplored planet of Troy, whereupon the ship's crew set up a thriving Frontier town in and around the ship's wreckage. This colony would go undisturbed for nearly two decades, until probes deployed into Sector Bravo-217 detected life forms on Troy while searching for the 1st Militia Fleet.
The opening stages of the battle involved scouting operations conducted by Kuben Blisk, who was given command of ground teams in the operation. Upon discovering the town, the IMC deemed it prudent to use the mutineers as a suitable test for the Second Generation BRD-01 Spectre eventually massacring all the colonists in Colony G21 who tried to resist capture.
An SOS message sent out by the colonists would be intercepted by the Frontier Militia, leading them to investigate. The IMC deployed three more squads of Spectres, and the fighting began in the streets.
The initial fighting between Militia and IMC forces took place in the streets of the town itself as Militia forces attempted to commune with colony leader MacAllan to find out what had happened.
Eventually, the IMC would decrypt the transmissions, leading them to learn of MacAllan's survival. With MacAllan's location determined as the hills around the Odyssey, IMC forces soon redeployed to prevent the attempted Militia evacuation of the colony. While IMC and Militia troops clashed in the skeletal remains of the Odyssey, Blisk would lead a team into the ship's bridge in an attempt to halt any transmission of data from the ship.
Ultimately, the Militia would succeed in buying time for the colonists to evacuate, gaining vital manpower for the cause including the ex-IMC officer James MacAllan, alongside a wealth of classified intel such as schematics for the Demeter refinery. These actions would be a turning point for the rebellion, putting them on the offensive rather than the defensive footing they had been on for months.
The IMC would capture many mutineers and colonists, sending them to Typhon to be experimented on by General Marder and ARES Division. They would also rediscover the remains of the Odyssey, the former IMC flagship in the Titan Wars with intent to salvage.
However, five years later as of the Battle of Typhon, Colony G21 has been rebuilt and the Odyssey practically remained untouched - indicating the IMC never got the chance to secure a foothold on Troy, and the planet became a Militia hideout.