Originally Posted by LapLap
BOAC used to have square windows, but 90 degree angles in a highly stressed pressure chamber wasn't a good idea and it cost lives (amazing they could figure out how to get all those tons of metal of the ground and not realise that - but then most things are obvious retrospectively),
You're thinking of the Comet I, rather than BOAC generically. You have to remember that metallurgy was then not really the science that it is now. The behaviour of metals was much less well understood. The causes of "metal fatigue" (as the phenomenon became known) were obscure, and this type of use of metal in a pressure vessel with this type of cutout was novel. We live and learn.