Right now when you discover advanced plane options you unlock WW2 era bombers. Those are fine for a pretty long time but eventually early jet fighters and jet fighters begin to have greater range and usefulness. then you jump straight into stealth flight. I think it would be better if you could remove the remote controlled stealth bombers and instead add a bomber to represent the transition from WW2 bombers to stealth bombers. A plane similar to a strato-fortress or something that uses jet engines.