It's not an "immune" attack. It makes it harder for the enemy to track you, but it also makes it harder for you to get a kill shot on the enemy. You can and will be shot down if the gunner knows what he's doing while making this type of attack. I have more than a couple of times. Barring a lucky pilot kill, it takes you a lot of sustained 30mm fire as you come down. Maybe I'm stingy, but I'd have used about 1/3 the ammo you did for each pass I made, at a slightly different angle.
It's a nice first attack, but don't plan on setting it up repeatedly if you want to stop the bombers before they kill your HQ, or kill your fighter hangars, or kill your CV. I think you were talking about taking upwards of 30 minutes to kill 3 drones. Let's be serious: you're making it too hard if you do it that way.
I'm the first to say "Dont' sit on his tail, you fool!" when I see that happen, but there are better ways. You would be surprised how effective a 2 o'clock or 10 o'clock slash attack is. It's also just as hard to track and shoot if done right (because the upper gun only aims down so far and the lower gun only aims up so far, the gunner has to jump up and down then left to right). It also leaves you in a much better position coming out the other side where you haven't just blown your alt and have to climb back up
