This airplane was part of an experimental B-29 modification program called "Project S68", which was a manned turret evaluation of B-29 type airplanes conducted in October 1944. The airplane used in the evaluation, B-29# 42-24441, was re-designated as a B-20-25-BW. The airplane featured manned turrets in place of remote controlled turrets as found on standard production model B-29 airplanes.
The airplane featured remotely controlled forward firing Emmerson Model 136 "Jowl Barbettes"-- one on each side of the nose and equipped with a single 50 cal in each barbette. The airplane also had two manned Martin upper turrets in place of the standard B-29 turrets on top. The airplane was equipped with two Sperry ball turrets--one was a Sperry A-2 Ball Turret mounted in the lower forward position and a modified Sperry A-13 ball turret in the lower aft position as featured in the photo. The airplane also was equipped with flexible waist guns. The program was soon dropped.