Wanting to try a few new things out in GSF, I bought a FT-3C Imperium strike fighter to use instead of the Rycer that you just get for breathing. But I can't access the Imperium when I queue for a match. It just isn't available to me to use. The Rycer is there, along with one scout, one bomber, and two gunship options, but not the Imperium.

I hope I'm not just being stupid, but what haven't I done to be able to use the ship I just spent req on?

you can choose which ships to put onto your bar. You can only have 5 on your bar at any given time.

in order to do this go to your hanger. (Default key for this is H), then click on the ship you want to take off of your bar (will have a yellow highlight around the ship), click the Select your Ship just above the ships, it will bring down a drop down list of your ships. Left click on the ship you want on your Bar. This'll move that ship to the slot you had highlighted.