the main role would be ground attack, like the skyraider in vietnam, but the only problem is that jet engine equipped aircraft are less resistant to ground fire. one lucky shot and the plane goes down. the mustangs in WW11 had this problem with there liquid cooled engines. the reason for the big old radial on the A-1 was that a radial can take a lot of hits and still keep running. the A-10 is really the only true ground support/attack a/c out there. we all know the kind of protection built into that bird, our PC-9 would need this aswell or the 9 aircraft would last all of 3 days in a real fight.
