[PeterVerney]

Fascinating stuff. Actually our pilots were taught deflection shooting on the Mosquito which had a fixed ring gun sight!.
The radius could be varied by setting the span of the target aircraft and so the range would be correct when the targets span filled the ring. With me so far; then pilots were taught to "lead off" by say "half a rad", or "one and a half rads", according to their judgement of angle off and closing speed.
If you have shot birds or game with a shotgun you will know what I mean. In fact we had a supply of shotguns, clay pigeons and ammo so that the pilots could practice. In addition we did many sorties of "cine", where aircraft flew in pairs and took turns to be fighter and target. High quarter attacks were the norm and cine taken when the pilot judged he was right. Then the films were assesed, frame by frame to judge how good the pilot was and he was criticised as required. I used to help our gunnery officer by doing some of this tedious work, in retrurn for a go on the clay pigeon shoots.
When we got the Meteor, with a gyro gunsight, of course things were much easier to assess, but as in all instances accurate flying was essential.
I must visit the NA again, I had no idea of all those references that's a goldmine. What I put down here is dredged from some recess of my antique brain.