Foreign tourism to Thailand was until the Second World War, and in the immediate postwar years, of modest proportions: in the 1930s, only about five cruise ships a year, carrying around 500 passengers, called upon Bangkok port. Tourism began to develop as an industry only in the late 1950s, during the dictatorship of Marshall Sarit (1957-63), within the framework of his general policy of development. Sarit initiated the creation of a physical infrastructure for tourism, established the Tourist Organization of Thailand (TOT, later Tourism Authority of Thailand, TAT), and encouraged foreign investment in the tourism sector. The most important boost for tourism, however, came later, during the Vietnam War, when Thailand became one of the principal destinations for R & R (Rest and Recreation) visits of American GIs. These visits were significant not only in terms of the increase in numbers of foreign visitors, but also as a principal factor of change of the touristic image of Thailand, and of the kinds of tourists which began to be attracted to the country from the mid-1960s onward.