Very few warships rely solely on beam weapons due to their short range. Some add torpedo tubes, but several rely on fighter craft to get the job done. In order to launch them, these carriers use fighter launch bays. These cannot be purchased separately but instead come pre-fitted to the hull.
A carrier may have anywhere from one to ten launch bays. Each has a chance to launch a fighter during any given moment of a space battle , but it's important to note that these chances are neither equal nor entirely random. A ship with one or two launch bays will launch very few fighters during an engagement (and so is generally referred to as a "fighter transport" rather than a "carrier"). The difference in combat power even between a ship with eight bays and one with ten is fairly large.
Starbases too have fighter bays. A well-defended, well-stocked starbase can destroy any torpedo battleship ever made, and it can go toe-to-toe with a heavy carrier in combat -- and against even the heaviest foe, it can sometimes win.
The fighter launch bay is the single most powerful offensive weapon in the game. All things being equal, it can take between sixty and seventy torpedo hits (that's a hundred or more launches) to destroy a heavy carrier, whereas the same ship can be destroyed by between twenty-five and thirty-five full fighter passes (that's about sixty to eighty launches on average, which come much faster and start much sooner).
The definitive article on combat, Master At Arms , was written in 1997 by Jan "Sirius" Klingele and is still almost 100% accurate. This is an offsite link, and Planets.nu is not responsible for the content.
See also: Combat