".... the greatest experiment in amphetamine-based enhancement came in World War II. In 1939 the
Blitzkrieg'ssuccess was attributed partly to the use of Pervitin—methamphetamine—among German soldiers. By mid-1940 the British and American militaries had begun their own respective chemical investigations. Both eventually settled on Benzedrine to combat fatigue and boost morale. The drug proved especially popular among pilots and air crews, who often had to fly long, grueling bombing raids late into the night. By 1943 a package of Benzedrine pills had its place in the emergency kit of every American bomber. Two years later a survey of European-theater fighter pilots who frequently flew long missions showed that around 15 percent frequently used Benzedrine.
SKF's advertising dutifully reported its new use among the country's fighting force. "For men in combat, when the going gets tough," one ad began, Benzedrine Sulfate tablets would save lives through "sustaining their mental efficiency by overcoming the symptoms of fatigue." Here, too, the evidence had proven inconclusive: the pills had slight to no effect on cognitive capabilities, but the "feel-good" effect often made users overestimate their own capabilities. At the same time, the nervous-system stimulation kept soldiers awake past the point of exhaustion, though often with dubious consequences, including hallucinations and paranoia, well-known effects of sleep deprivation and amphetamine use.
Methamphetamine produced similar results; ironically, the accompanying recklessness, along with worries about addiction, quickly led the Germans to discourage its use in the field. American and British forces, however, used amphetamine throughout the war for its effects on mood and morale: it kept up the "fighting spirit." The British later concluded the subjective boost wasn't worth the potentially lethal side effects, but the American military continues to use amphetamine to this day, including in the conflicts in Iraq and Afghanistan."
Fast Times: The Life, Death, and Rebirth of Amphetamine | Chemical Heritage Foundation