Boeing B-17 Flying Fortress B-17C

The B-17C introduced more powerful Wright R-1820-65 engines, replaced the waist machine-gun blisters with flush sliding panels, and swapped the ventral blister for a metal gondola nicknamed the "bathtub". Its most important additions were self-sealing fuel tanks and armor plate. It first flew in July 1940 and 38 were built; those that stayed in Army service after 20 went to the RAF were mostly upgraded to B-17D standard. As the Fortress Mk.I, the RAF's 20 aircraft performed poorly in Britain — nearly half their sorties were aborted for technical failures and eight were lost within months.