The B-17E was an extensive revision of the Model 299 design: The fuselage was extended by 10 feet ; a much larger rear fuselage, vertical tailfin, rudder, and horizontal stabilizer were added; a gunner's position was added in the new tail; the nose (especially the bombardier's well-framed, 10-panel nose glazing) remained relatively the same as the earlier B through D versions had; a Sperry electrically powered manned dorsal gun turret just behind the cockpit was added; a similarly powered (also built by Sperry) manned ventral ball turret just aft of the bomb bay – replaced the relatively hard-to-use, Sperry model 645705-D B-17 Erection and Maintenance Manual 01-20EE-2 remotely operated ventral turret on the earliest examples of the E variant.