FW,
Flying an aircraft is relatively easy - operating a highly complex military aircraft in a variety of roles with advanced sensors, weapons, comms and, doubtless, different flight regimes is very difficult. To use Tourist's approach above, could a CPL(H) fly a Chinook? Absolutely, it's actually a very simple aircraft to fly (AFCS in....) and he/she could probably hover and fly a circuit in very few minutes. Now, take that CPL(H) and ask them to fly at night, on NVGs, at low level, in poor weather, in a hostile EW environment and risk being shot at in the landing zone....well, I don't recall many of those skills being on a Commercial syllabus. I imagine for the P8 there is still a requirement to fly low level over water for various tasks, and to deal with a very complex weapon system (albeit with help). In short, conversion to type can be pretty straightforward, conversion to to role and achieving Combat Ready is an entirely different matter and where most of the expense is. However, if there were ex-Kipper fleet guys out there currently flying the 737-800 it might help to have a RAuxAF flight in the early stages to help build the available front end pool. My guess is that the pinch point is actually going to be with the highly specialised rear crew, only so many of which went on seed corn or remain in the RAF......