Fall of the Twelve Colonies

Battle before: First Cylon War
Concurrent Battle: Fall of the Scorpion Fleet Shipyards
Battle after: Battle of Ragnar Anchorage

Caprica during the Cylon Attack Caprica during the Cylon Attack Cylon nuclear bombs detonating on Caprica
Fall of the Twelve Colonies
Conflict	Second Cylon war
Date	Zero Hour
Place	Twelve Colonies of Kobol
Result	Decisive Cylon victory, occupation of the Twelve Colonies
Combatants Twelve Colonies of Kobol Cylons Commanders Admiral Nagala † Commander William Adama Unknown Strength Approx 120 battlestars, Vipers, Raptors, associated support cruisers Unknown number of Basestars, Raiders, Heavy Raiders Casualties All but 2 Battlestars, near-total devastation of Colonial Fleet and civilian population Unknown, minimal

The devastating opening wave of the Second Cylon War, in which the Cylons used a programming backdoor to infiltrate and shut down Colonial Fleet systems. Most of the ships that tried to engage the forces of the Cylon surprise attack suffered immediate and total power failure, "like someone turned off a switch". The only Fleet units able "to make any progress at all" against the invading Cylons were those who were older or overdue for maintenance (essentially those that lacked the compromised software), and there weren't enough of them to make a real difference.

Battlestar Galactica, commanded by William Adama, was the only Colonial ship unaffected by the Cylon's computer infiltration, because it's computer systems were never networked. Though Galactica lost all 20 of her Viper Mark VII's in their first sortie against the Cylons because their networked computers were vulnerable to infiltration, she also had 40 Viper Mark II's board as part of its recent decommissioning ceremony. The Viper Mark II's were an old but robust design, but most importantly never contained the Command Navigation Program that doomed other fighters and were therefore unaffected by the Cylon computer virus. Galactica was able to re-arm and deploy its Viper Mark II's and repel several attacking squadrons of Cylon Raiders, even surviving a direct hit from a Cylon tactical nuclear warhead, but not without a loss of 85 of its ship's crew in the port flight pod and some internal damage.

The Cylons proceeded to use nuclear weapons against each of the Twelve Colonies, including Caprica. After Picon was nuked, the Colonials broadcast an unconditional surrender, which was completely ignored by the Cylons. President Adar and all Colonial government officials, save for spacebound Secretary of Education Laura Roslin, were presumed killed or missing. The Case Orange contingency mechanism activated to seek out the remaining government officials, of which only Roslin apparently acknowledged. Sworn in on the government passenger liner Colonial Heavy 798, she became the new President of the Twelve Colonies. Roslin immediately began locating other stranded Colonial civilian and military vessels to form a convoy. Several ships without faster-than-light ability had to be left behind to their fate by the other FTL ships of the convoy when the Cylons located the convoy and an attack was imminent. These sublight ships and their passengers were destroyed by Cylons while the remaining ships joined Galactica at her new location.

Picon Fleet Headquarters was destroyed in the opening wave of the attack, as were 30 battlestars, noted to be "a quarter of the Fleet" according to Kara Thrace's comment to Commander Adama in the opening events of the attack. Admiral Nagala subsequently took command of the fleet aboard battlestar Atlantia. Soon after, Atlantia was lost with all hands. Commander Adama aboard Galactica assumed command of whatever was left of the Colonial military fleet, and sent a wireless transmission to any surviving Colonial forces to rendezvous at Ragnar Anchorage where desperately needed munitions were stored for the battlestar's guns and her fighters.

Battlestar Pegasus escaped certain destruction by the Cylons at the Scorpion Fleet Shipyards by a making a blind jump into space. Most of the battlestar's networked computer systems were offline for an overhaul except for her navigation computer, which fortunately could execute a Jump. With the "fog of war" and the desperate means of their escape, Pegasus was apparently unaware of Galactica's survival and proceeded to conduct attacks on Cylon forces it encountered as it, too, left the solar system of the Colonies. Galactica had no knowledge of this other battlestar as the Colonies disintegrated and communications between other Colonial forces faded into static.