The full history of the Fortress Mk.I (B-17C) is described. This was somewhere an experiment led by the British under the secret supervision of the Americans. Many lessons were learned by the RAF but the British eventually discarded the Flying Fortress as a day bomber, what the Americans decided to ignore. Over 30 photos, 2 colour profiles. An update and revised edition of Allied Wing No. 7. Revised November 2019, February 2022. The history of the Fortress Mk II and Mk III is detailed in SQUADRONS! No. 21.