The Battle of Casmoro Acapellico was actually an ambush on the Fourth Fleet by the Cylons. The fleet, under command of Commander Kronus in the Battlestar Rycon was undertaking border patrols along the Colonial Border, when they were ambushed by a large Cylon task force in the Acapellico. The fighting was heavy and casualties on both sides were high.
The Fourth Fleet managed to break out of the ambush and retreated back to the Colonies. Although severely mauled, they inflicted serious damage on the Cylons, destroying some 3 Baseships in the process.
This was the end of the Fourth Fleet though, and it was split up on return, the majority of the surviving heavy elements being drafted into the Fifth Fleet.
It is interesting to note that the Fourth Fleet consisted of some 600 combat vessels.
The Fifth Fleet under Commander Cain, was completely destroyed here, or so it was thought. The Battlestar Pegasus escaped into deep space and for two yahren battled the Cylons in their own space at Gomoray.
The idea was that the Fifth Fleet would begin a series of counter offensives against the Cylons, with the aim to tie up Cylon Fleet elements, disrupt their command and control, and destroy as much as they could possibly could. Then, the Fleet would return back to the Colonies. Success would allow the Colonials time to regroup, rearm and bring the offense back to them. As this was going to be a major counter attack, the Fifth Fleet was assembled of almost all the remaining heavy cruisers, destroyers and other capital ships, and thus was a major gamble. If the plan failed, would there be enough of the fleet to return and stem a Cylon attack? As such to assure success, most bases and other fleets were stripped of their ships to form the Fleet, leaving a skeleton force of a few Battlestars and supporting light cruisers and destroyers behind. The fleet was indeed grand.
The first phase of the offensive was to liberate the system of Molecay. Unfortunately, the fleet entered the system of Molecay and never reported back. Survivors were not forthcoming, and the whole fleet was deemed lost. It is known that that Fleet left a trail of Cylon Destruction in its wake, but it seems that the Cylons had the upper hand in the end.
The Cylons did momentarily pause their advance, but the Colonials did not have enough time to take advantage of this.
It would later be known that there was one survivor of the battle - the Battlestar Pegaus, flagship of the Fleet and commandered by the legendary Commander Cain. Cain managed to escape the battle somehow, and instead of returning to the Colonies, he vanished into deep space, to resurface at the Cylon Southern Capital of Gomoray where he was raising hell, striking at the base there and taking fuel and supplies when needed.