How had warfare changed during World War 1 to increase the threat to Britain in World War 2?
WW1 had shown how very vulnerable Britain was to hostile
submarines in the Atlantic, and the development of bombers had made
much of Britain vulnerable. After the fall of France, the enemy was
much nearer and could easily use airfields in Belgium and France.
The whole coastline opposite Britain, from the Arctic Circle to the
border between France and Spain was in enemy hands. Joncey