I talked to a B-17 crewman at an airshow about this. He remarked that that they shot themselves up all the time. I asked him "how could that be, didn't their .50s have stops so that they couldn't be pointed at their own plane?" His response was just as you indicated. "Yes, but when you're shooting at someone trying to kill you, you don't stop even if he's on fire and tumbling out of control. You continue shooting reflexively, and if one of your formation gets in the way, that's too bad."

Fotunately, the B17s could absorb a lot more damage than Bf 109s or FW 190s. So they usually made it home, maybe with a few friendly holes in them.

We had a chopper on board the Dewey whose job was to rescue flyers that had been shot down by N Vietnamese air defense. (They picked up two, and we fished a third out of the water ourselves).

Our first chopper had to be replaced, because on its first training mission, they shot themselves down! The door gunner didn't properly adjust the stops on his M60 and a round nicked the tip of the rotor blade while they were shooting at practice targets in the water. An unbalanced vibration shook the chopper to pieces and it had to crash land in the ocean. Fortunately, they managed to get a signal off before they sank and we were able to rescue the crew.