Why the first pilot test jaeger, was a USAF pilot and not a Ranger ??
Why the first pilot test jaeger, was a USAF pilot and not a Ranger ??
Because "Rangers" didn't exist yet. No one knew if Jaegers would work, so they used test pilots.
Well, they probably did some training before they put him in the actual Jaeger, so it's not like they expected his airplane piloting skills to translate over perfectly.
Furthermore, test pilots, by their very nature, are used to unfamiliar and untested equipment. Also note that the Drift was based on jet neural interfaces.
The Jaeger Program was a truly international effort. Even countries that weren't directly threatened, like the UK, contributed to stopping the Kaiju, hence why British pilots might have been involved.
(Also because BRITANNIA STRONK but that's neither here nor there.)
As to the RAAF, Australia was a front-line nation, or Striker wouldn't exist.
Plane pilots are used to controlling vehicles in solos or duos (rather than large teams), and they have an existing job called 'test pilot,' ones who specialize in trying out new things. So, using 'em for tests makes sense, before they were able to make a proper jaeger-specific training program.
And I bet even once there was a proper Ranger program, a lot of pilots were the type to try out for it.