This was the Blitzkrieg, a devastating tactic combining quick movement of troops, tanks, and massive use of air power to support infantry movements. And in the very early years of the war, it was extremely effective. The Nazis were able to roll over Poland, Norway, Denmark, the Netherlands, and then all of France, all within about nine months between the fall of 1939 and the summer of 1940. So after knocking out most of Central Europe, the Nazis set their sights on Great Britain. But they didn't invade the island, choosing instead to attack it with massive airstrikes. I mean, you look at this poster and think, man, the Queen wants me to finish my term paper so I can do it. But when this poster was first produced in 1939, it was to quell terror in the face of bombardment.