For nearly 20 years, from 1955 to the mid-'70s, the American military was thrust into the jungles of Vietnam. The war took an emotional toll on American troops that, in many ways, outweighed the physical strains of battle, and soldiers coped through drug use, primarily heroin. Not only did it blur the hell around them to a manageable haze, it was something to do that didn't involve death and destruction, at least not initially. Many of the men who returned home were hooked for life, unable to cope with the world around them without a veneer of smack.

There was no shortage of mind-altering substances in Vietnam during the war. Soldiers were plied with more booze than they could drink, and thanks to the lax drug laws in Vietnam, marijuana wasn't hard to get, either. Studies show that more than 50% of soldiers smoked marijuana and an additional 28% of them were using heroin. With a little more than nine million soldiers serving during the war, that's just under two million soldiers using one of the most addictive drugs known to man. Those numbers are just estimates, but they show how widespread illicit drug use was throughout the military during one of the worst conflicts in U.S. history.

Ironically, many soldiers started using heroin because of the crackdown on less harmful drugs. As drug use increased across the board in Vietnam, the country's laws became stricter, and the U.S. military came down harshly on their soldiers.