".....the guns will not be used as a routine part of training becasue of the deleterious effects on the airframe/avionics, etc of the vibration, etc from the weapon - but
if the aircraft is deployed to a war zone, the work up for the crew will include air firing of the gun"
So, just before you go to war, you learn to fire the gun. Bit of a bugger if it's only then that the true 'deleterious effects on the airframe/avionics' come to light and all the C/Bs go pop or whatever the computer equivalent is.
But, with a Canon, you can take some nice piccies of the opposition you should really be hosing with HE!