To quickly and Easily Destroy Anti-Aircraft Guns using a Helicopter in Far Cry 6, when you get the call from an operator letting you know you are not allowed to be flying in an area, get back out of the zone and descend until you are very close to the ground. Be sure to mark the anti-aircraft gun on the map and then stay very low and fly towards the anti aircraft gun.

Once you are there, destroy the anti-aircraft gun using the missiles on the helicopter. You can then clear out any enemies or land and collect the depleted uranium.