The list is huge in the campaign, you get to fly fighters and bombers, man gun turrets on the ground etc. I don't have a list to hand.
But you get to fly some of the large bomber briefly too, or man the guns.
In instant action you only get to fly the fighters or the more mobile 2 seaters (no Gotha
The names of the planes are odd abd I won't quote them here but the actual types are something like:
Walfisch 2 seater
ALB CIII 2 seater?
Seaplane (don't have the type to hand)
Experimental Alb triplane
Fe2b or gunbus (it's called Gunbus but looks more like an Fe2b to me
Bristol F.2B 2-seater fighter
Re8 2 seater
Breg14 2 seater
Nieup. Experimental triplane
maybe 1 or 2 more?
In instant action your plane choices expand as you do better in the campaign. You get to "unlock" more. There's a "cheat" game save you can download that lets you access all available fighters without completing the campaign, but there are many planes like the bombers you don't get to choose from still.