Great pic as always, Jack!
As Luftwaffe opposition diminished late in the war, many B-17s and -24s had the ball turrets removed to save wieght. Some -17s even had the chin turret removed as well.
I talked to a B-24 crewman once who'd been a ball turret gunner. He said that late in the war they removed the turret, and made him a bomb "togglier" (only the lead ship in the formation carried a bombardier and bombsight..everybody else would toggle their bombs at his signal.)
I've seen several color photos a formation of Forts from that same bomb group. I wonder if the pics were shot during a practice mission. That could explain the lack of tail gunners.
SN