The Vietnam War (1959-1975) was the longest military conflict in US history, and the war held many unpleasant surprises for the Americans. Not least among these was the widespread use of drugs by US troops. By 1970, almost every enlisted man in Vietnam was being approached by someone offering him heroin - usually within the first few weeks of his arrival in the country. One soldier described how his first offer of heroin came, as he was leaving the plane on which he had arrived in Vietnam, from a soldier preparing to board the same plane to return home. By 1971, it had been estimated that almost half of the enlisted men serving in Vietnam had taken opiates (mainly heroin) on at least one occasion. Most of those who used opiates used them repeatedly and over a long period, and most of the troops who used drugs while in Vietnam used more than one type. Amphetamines and barbiturates were both widely used, and some estimates suggest that more than three-quarters of the troops in Vietnam smoked cannabis. As many as 20 per cent of the troops reported that they had been addicted to opiates. This was a cause of considerable alarm to both the military and civilian authorities. At a time when the defence of South-East Asia against the communist menace was felt to be essential for the maintenance of the American way of life, it was not reassuring to hear that a substantial proportion of the fighting troops were using heroin. Nor was there much comfort in the thought that tens of thousands of heroin addicts might soon be discharged from their duties in the killing zones of Vietnam onto the streets of the US.