The fake 8-inch gun that fooled an exercise

What is a memorable example of service personnel making an unauthorized field modification?

British recovery-vehicle crews mounted a fake 8-inch gun made from pipe, then used the exercise rules to register kills with it.

British beach armoured recovery vehicle crews on a 1980s exercise disliked being the only armoured vehicles without a gun. They fitted a large section of pipe to one vehicle and persuaded the exercise system to register it as an 8-inch weapon. Once the notional gun could score kills, the recovery vehicles began destroying opposing units on paper. The exploit exposed a weakness in the exercise rules and forced the controllers to reassess what counted as a valid engagement.