The infamous Basestar was originally a large carrier for Raiders and Cylon ground assault troops, although the term "Barge" might be more appropriate as the Basestars were poorly armoured and relied on their long range missile firepower and massive numbers of Raiders to deal with enemy threats and if something got through, it was sufficiently large to absorb even major hits. At worst a few hundred Cylons could be destroyed, they were after all ... disposable.
Though Battlestars were originally designed to be superior to Basestars, the Colonial Fleet was in for a rude awakening. Nearly all rebelling Basestars were destroyed in the initial fights, leading Fleet Command to believe the war would be over in a matter of weeks or months. But when the Colonial Fleet went beyond the Red Line to search for the surviving Basestars they met something unexpected. For years the Cylons has secretly been building installations on distant planets and moons, building new, more powerful Basestars that were much more advanced than the original designs. Outwardly identical to the first generation they were better armoured and compartmentalized to reduce internal damage. They had been redesigned to carry more Raiders and most importantly the slow, lumbering Basestars with limited jumping capability were now fast and deadly raiders that could attack any Colony World. Colonial forces were suddenly pushed on the defensive and stretched to the limit in trying to protect the Twelve Colonies and many more outposts and orbital cities. In order to strengthen their defenses the Colonial Fleet had most outposts evacuated and millions of people were on the move to safer worlds within the umbrella of the Fleet's jumping range. A few refused to leave and remained behind, but their outposts were soon overwhelmed by the Cylons.
The fact that a Basestar could appear at any time in orbit around a Colony World came as a shock to most people. Even if a single nuclear got through it could kill millions and the Colonial Fleet did not have the capacity to fight an extended campaign beyond the Red Line. Early struggles were bitter defensive battles such as the Two Battles for Caprica as well as the terrible ground fighting on Aerilon, Saggitaron and Libra.
The First Battle for Caprica proved to be a turning point. The seemingly relentless Cylon onslaught ground to a halt. For the first time it became clear to the Colonials that the Cylons did not have limitless resources and Basestars. Their gamble to destroy the richest Colony had failed and they began to regroup and rebuild, giving the Colonial Fleet some breathing space.
Desperate to strike back, the Colonial Fleet gathered Task Force Brimstone also known as the "Invincible Armada" under Admiral Irinia Murata. Five Battlestars, three Gunstars, two Missilestars and a dozen strike- and skirmishstars. The plan was to destroy a major Cylon shipyard, which in fact was a carefully laid trap. Battlestar Acropolis sacrificed herself so that Murata's command ship the brand-new Battlestar Longbow could escape. Her final fate is unknown to this day.
But even if the Cylons scored a major victory that day they never were able to pose such a threat as First Caprica. The war went on for nine long years and became a series of raids, trying to catch the other unaware. In the closing days of the Cylon War the Colonial Fleet had dramatically expanded and had more than enough Battlestars to conduct extended operations deep into Cylon territory, forcing them further back into space and leaving the Colonies less vulnerable to attack. The Cylons did fight for every planet, moon and asteriod, exacting a high cost. When after twelve years of warfare the Cylons suddenly offered an Armistice the Colonies gladly accepted.
According to declassified records the Cylon Fleet had been reduced to little under a dozen Basestars, while the Colonial Fleet had nearly 40 Battlestars and more than 200 other ships with many more being built.
Today the Colonial Fleet boasts nearly 120 Battlestars and ten times that number in Gun-, Skirmish- and other Strikestars. The Cylons have been pushed back to the Armistice Line, an area of space sufficiently deep to prevent their ships to reach the Colonies in less than three jumps. Automated listening stations with relay jump couriers would warn the Battlestars guarding the Line of an impending attack and give the Colonial Fleet ample time to muster her considerable strength and stop the Cylons before they could reach any Colony.
The Cylon war cost nearly 65 million casualties the vast majority of them civilians. Of 80 Battlestars built during the war, nearly half were destroyed.