All the above means that models of warfare should be taken for no more than they are: a non-prescriptive attempt to inform the decision-making process. The dangers of treating military simulation as gospel are illustrated in an anecdote circulated at the end of the Vietnam War, which was intensively gamed between 1964 and 1969 (with even President Lyndon Johnson being photographed standing over a wargaming sand table at the time of Khe Sanh) in a series of simulations codenamed "Sigma". The period was one of great belief in the value of military simulations, riding on the back of the proven success of operations research (or "OR") during World War II and the growing power of computers in handling large amounts of data.