It's a matter of experience, redbeard.
For carriers, at level 1, you get 2 squadrons + 1 additional squadron for every two experience levels up to level 10. (3 at level 3, 4 at level 5, 5 at level 7, etc.)
You can buy your first two experience levels (and more with certain expensive research), but it costs a lot of money to do so.
A level 10 carrier with six squadrons is a pretty powerful aide to your little fleet.
-- Retro
