The RAF's Fortress Mk. Is were the first Boeing B-17s to see action in Europe during World War II. This was made possible by two different but complementary requirements. The British were looking for another way to bomb Germany and Occupied Europe by day and the Americans wanted to see how their bombing strategy would work using the B17, and the resulting tested limits of this strategy - of which the B-17 had been designed specifically for this purpose. The Americans, who were always in the background of the European evaluation, and also in the Middle East, played a vital role in the RAF's operational trials in 1941. The results were poor and most of the lessons learned were simply ignored but here in 40 pages the full career of the Fortress I is recalled. Illustrated with 35 photos, some seen for the first time, this booklet gives historians all they need to know about the Fortress I.