Boeing B-17 Flying Fortress B-17D

The B-17C and B-17D shared so much (the same Boeing 299H company designation) that only minor changes justified the new letter: adjustable cowl flaps, removal of the external bomb racks, a revised electrical system and a tenth crew position. A twin-.50 mount was added in the radio compartment and another in the ventral position, along with extra armor, bringing total armament to seven guns. 42 new airframes were built and the remaining 18 B-17Cs were brought up to the same standard. The sole surviving D, "Ole Betsy"/"The Swoose", is preserved under restoration at the National Museum of the USAF.