From the article:
"For our soldiers in Vietnam, something so honest and everyday as a lighter became a powerful token of pre-war life, and a way to express their frustration, fears, and loathing over the war. These young men were sent into Charlie’s jungle to fight an invisible enemy, over a conflict that many didn’t trust or understand– and about the only items they could take with them from civilian life were a wristwatch and a lighter. The Zippo became a symbol of their souls."
read the full article here