I was fortunate enough to do a ACPNS course at RAF Shawbury back in '89. All you had to have do back then was pass the ATC Air Navigation exam and then do all the aptitude stuff at Biggin Hill before being offered a place. I spent two glorious weeks in the back of a Chipmunk navigating around the Welsh Borders and making tea for the AEF pilots. Did also manage to scrounge a Puma trip! Essentially my course sounds the same as Flarkey's experiences although in the Chippie you could only visually tell where you had been and not where you were heading to! 1 in 60 rule, using a Dalton Computer, diversions, fuel loads, met, etc. All good stuff. I assume the course would heve been modernised a tadge and you get to use GPS but I am not sure. In summary go for it. There aren't too many in the ATC who ended up with a half brevet.