Recently, I saw the move Memphis Belle on Blue-ray. When I saw the movie, I noticed there was a hatch over the ball turret that had to be locked and could only be opened from the top. I was wondering why this was, because as seen in the movie, the gunner could be trapped in there, hanging for his dear life. My Dad thought it was so other crew members couldn't fall in, but that doesn't explain why the hatch was locked. I hope you can answer this. :)
The hatch had to lock shut because the ball rotates, if it came loose it could get jammed and/or expose the gunner to the outside (and enemy fire).
Pic here http://www.ww2incolor.com/us-air-force/B-17ball-turr-42.html Imagine the gunner directing the guns downward, to shoot an enemy aircraft below him, the hatch would now be at (say) the 10/11 o clock position instead of the 7 or 8 o clock position it is in that picture. You can see the hatch becoming exposed in this video: https://youtu.be/CIjWW9HQCzw
The ball turrets were a dangerous place to be - gunners did get stuck in them and I remember reading one account of a gunner being stuck in one and the aircraft having damaged undercarriage, resulting in the need for a belly landing. Just horrible. It seems that there is no official recognition of this, but eye witnesses claim it did happen. A few threads out there on the subject: http://boards.straightdope.com/sdmb/showthread.php?t=759847
http://www.ww2aircraft.net/forum/aviation/story-heroism-trapped-belly-turret-gunner-29968.html
http://www.usmilitariaforum.com/forums/index.php?/topic/156203-crushed-ball-turret-gunner