During WW2 German soldiers were taking a "medicine" called Pervitin, this stimulant contained pure methamphetamine, which we know today as crystal meth.

"The Wehrmacht found out that Pervitin reduces fear, it reduces your need to sleep, and it makes you more aggressive. So these three reasons seemed perfect for the German army in 1940:" Norman Ohler, author of "Blitzed: Drugs in the Third Reich" told Business Insider.

"Drugs came into play for example for the army in the war as a sort of pharmacological weapon, just as they used real weapons to fight.

"Churchill said to his French colleague Daladier, when the Germans attacked, he should not worry so much about the speed of the German army because after 12 hours they would have to rest. But the German army, being high on methamphetamine, didn’t have to rest.

"Churchill didn’t know about this so the first three days and three nights the Germans made huge advances by just not stopping and surprising the Western Allies this way."