When pulling sentry duty at an active small arm's range, close to a military airfield, we were given a Very pistol loaded with a red flare. We were told that when the Buldog trainers came over, if we could read the reg, fire the flare as they were breaching the 500ft safety exclusion.
No idea if that's right, but thems was the orders.
I spent many hour WILLING one to be low enough to give me the excuse!
Sadly.................... nooooooooo!!!!