B-17E
On the first 1/5 of the production run, the B-17E was equipped with a ventral remote-controlled Bendix turret, similar to that on the B-25 Mitchell.The production was too much for the Boeing factories to keep up with, so Lockheed and Douglas also produced the B-17E. Douglas built a new factory for the production of the Flying Fortress, and Boeing built an additional factory just for the
production of the B-17.