zxcv wrote:

It looks to me like the B-17 had more forward guns than people to fire them.
According to my count there were two men in the forward compartment
(bombadier and navigator).

Looking at pictures of the B-17F Memphis Belle I see four guns, each in a
separate loophole in the nose of the plane.

Looking at pictures of B-17G's I see 2 cheek guns and the chin turret.
Another picture shows the bombadier's area and he has a cheek gun position
and controls for the chin turret.

Did they switch to whatever gun had a target in range?

Yes. The bombardier normally manned the nose gun(s) (flexible or later turret),
while the nav. manned the cheek gun(s), switching from side to side as
appropriate. Oh, and trying to keep his nav. log up to date, recording kill
claims, etc.

Guy