Not in the ToD. The airforce isn't exactly like a mercenary force

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According to what we've seen, the ToD HTC has envisioned is an online campaign mode comparable to those in boxed games, or one of those Coop missions in IL2/FB - except unlike boxed games, almost all participants are human players, and unlike IL2/FB Coop, it isn't a single event - a systematically organized flow of events and missions based on real historical time-line.
Plus, an RPG aspect which simulates and rewards player experience and leadership in the form of progression of rank, and simulating the military aspect with an internal chain of command. Maybe some other RPG style goodies for immersive experience.. etc etc.
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So, it's gonna be the other way around
Choose what mission you want to fly, and that will decide what plane you can use. A ground attack or interdiction in 1943, and you'll get to join either a mission with P-38s, or another mission using P-47s..