3 The need for armour and self sealing tanks was seen as soon as combat was started, you don't notice it in peacetime war games because you didn't actually fire live ammunition. ... Why advise your enemy that you are using it in France when a plane is captured?
As tomo pauk said the move toward armouring planes started in earnest months--and in some cases well over a year--before the war started (in Britain).
Blenheim and Hurricane squadrons based in France used 100 octane.