They also used to train a few up as 'split brains' - two trades plus the ability to operate the back cockpit as a pax. They were very useful for taking abroad to fix snagged jets to get them home, rather than having to send out a full team slowly.
Although having the nav kit/computers dump just after takeoff into harry doggers weather over, say, Belgium was not my idea of fun, and happened more than once. Nevertheless, flying head down and thumbing along a chart came back to me
reasonably quickly, whilst twiddling with VORs & reading En Route Supp.s is of course why the RAF recruits pilots with 3 hands and two pairs of eyes.
At least they managed to fix the jet every time.