I agree with Sax.
Ghosth, although the plane WOULD be able to do it (erm, maybe, depends on the pilot and the specifics of the day along with the aircraft and it's condition, a lot of variables), the CREW could not. Here is a picture of a B-24 waist turret...
Tell me, if the plane goes vertical, what happens? Gravity says, they fall. They fall, and more than likely, get hurt or crush the tail gunner. Now, after your done falling, what happens when that plane goes up-side-down? You fall again. Now, you also had ammo boxes and other misc. loose items, which, yup, you guessed it, as gravity says, they fall too. Now, what happens when you fall, then have 150 rounds of ammunition, stored in a box, fall on your arm? Your arm hurts like hell. So, you just fell, crushed your tail gunner, had ammo fall onto your arm, you're in not-so-great shape. Now, while the plane is up-side-down, shoot your waist gun...
Oh wait...
You're hurt, and odds are, you won't be shooting the waist gun if you needed to, even after leveling out...
You wanna do it? Fine I say, but say good-bye to your gunners...
My $.02.
~Trig