Don't the Americans still have an Air National Guard that works in a similar fashion to our VR or TA over here - a kind of part-time military backup which can be called upon in emergency? I'm sure I read that many US civilian pilots are also members of the ANG, which might account for driving an airliner one day and a military type the next..
An ATC friend of mine is in the RAFVR and often bombs about in helicopters, but I don't think as a pilot..