During WWII, the U.S. military realized that if fighter pilots didn't get sleep, their poor decisions had dire consequences. Their mishaps included errors that resulted in their being shot down--or shooting down guys on their own side.
Helping combat pilots get good rest fast became a priority. So the military brought in naval ensign Bud Winter to develop and test a scientifically designed method of "teaching" sleep. After just six weeks of practice, 96 percent of pilots could fall asleep within 120 seconds.