Abstract :
Fifty years ago last month, US president John F. Kennedy said that Nikita Khrushchev, the leader of the Soviet Union, had made an empty boast about his country\´s antimissile missiles. "What you are trying to do is shoot a bullet with a bullet," Kennedy said, coining an oft-repeated phrase. "Now, if you have a thousand bullets coming at you, that is a terribly difficult task which we have not mastered yet, and I don\´t think he has. The offense has the advantage."