The Battle of Dawn City was the last major action during the Sunrise War, and was an attempt to break a fourteen-month siege.  The Southern Alliance, gradually worn down by a protracted conflict with the United Imperial Worlds, found that its supplies on Dawn would  be depleted within weeks.  Fresh supplies were scarce, as the Imperial Navy maintained almost constant control of the Sunrise system since the sixth day of the war.

Desperate for a quick victory, the military leaders of the Southern Alliance Army (SAA) settled on a desperate plan.  A single nuclear device would be detonated over the city.  In the resulting confusion, they believed, a sizable invasion force could land within the remnants of the city.  This SAA force was expected to push outward as the siege forces pushed inward, trapping the Imperial Army defenders.  However, if the invasion force could not push outward quickly enough, it might be all but destroyed by the high radiation.

The nuclear device was detonated at noon on 14 October 2343, and the the subsequent invasion began an hour later.  The Army command structure, based in Dawn City, was utterly destroyed.  However, the Imperial Army forces were largely spared by the blast itself, as the lines of defense were well outside the city.  The invading SAA divisions thus found themselves dramatically weakened by radiation poisoning when they first engaged the Imperial Army.  The remaining officer in command, General John Paul Windsor, ordered the Imperial Army forces to split.  His outermost lines would hold position against external assaults.  Reserve troops were sent inward to meet the invading divisions as they emerged from the blast zone.

The invaders were utterly destroyed by the fresh Imperial Army Reserves.  Several hours later, the Reserves later joined the defenders in breaking out and routing the remainder of the Southern Alliance Army.  Enemy facilities were bombarded from orbit by the Imperial Navy, effectively smashing the SAA altogether.  An armistice was signed the next day.