Come on in, the water's lovely.
In my not inconsiderable time in the RAF I have known many people who have transferred from the Army or Navy to the light blue (of my last 3 bosses 1 was ex dark blue and 1 ex brown) but I can't recall anyone going the other way. I don't know if there's much traffic between the other 2 Services either.
It would seem to me that people either made the right choice initially or have finally come to their senses and joined us later in life. It would make scrapping the RAF so disappointing for so many that we really should resist it on humanitarian grounds alone.