The Colonial Fleet is either the primary or a large armed service branch of the Colonial military, under the jurisdiction of the Ministry of Defense. The fleet operates in tandem with another branch of the armed services, the Colonial Marines.
The Fleet was presumably based at Picon Fleet Headquarters, and was under the leadership of Admiral Nagala at the time of the Cylon Holocaust. Other identified Fleet installations included the Scorpion Fleet Shipyards, Ragnar Anchorage, and the Armistice Station.
Known Ships
By the time of the Cylon holocaust, the fleet included approximately 120 battlestars. The existence of Battlestar Groups strongly suggests that there were other military vessels in support roles, akin to an aircraft carrier battle group.
Ships mentioned destroyed in the Cylon Attack included Triton, Solaria, Columbia, and Atlantia, commanded by Admiral Nagala. According to Admiral Helena Cain, two battlestars and three other ships (type unknown, but presumed military vessels) were destroyed in the Fall of the Scorpion Fleet Shipyards.
Currently, the only two military vessels known to have survived the attack are the battlestars Galactica and Pegasus.
Notes
In the Mini-Series, William Adama tells Kara Thrace when she's released from the brig "We lost 30 battlestars in the opening attack". She responds, "That's a quarter of the fleet". This establishes that there were approximately 120 active battlestars at the beginning of the Mini-Series.