From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
The "Big G" is a nickname, often used by the Viper pilots, for Galactica.
For instance, Kara Thrace uses the nickname when chiding Dwight Saunders on his landings (TRS: "Bastille Day").
- Nicknames made from the first initial of a ship are common for aircraft carriers in the US Navy. For example, the aircraft carrier USS Enterprise was nicknamed "The Big E" during World War II. Its nickname carries on today, where a large "E" is painted on the conning tower of CVN-65, the nuclear-powered successor to the WWII-era carrier.