I am finding that, when you fire from a gunner position on the Ki-67, that is the only gun that fires. In other words, the drones and any other guns with line of fire on the target do not also fire. So, our defensive gunnery is 1/3 (or less) of what it seems should be.
At least this is how it is for me.
To test it, go into the arena, take up some Ki-67's, fire a gun. Notice that other guns do not seem to be firing. Jump into the other plane and look at the ammo count -- no ammo will be expended.
Unfortunately, the scenario that is running (Operation Downfall) has Ki-67's in it as the main Japanese bomber. I'm feeling a lot less secure (being one of those Ki-67 pilots).
