The answer came the next day, from signals intelligence. A Navy SIGINT direction finding net in the Atlantic located the Soviet ships by intercepting and triangulating messages that they were sending back to the Soviet Union. The ships were stopped dead in the water, outside the ring of American naval vessels waiting for them. A confrontation had been averted, one that might have precipitated war. The president, his cabinet, and the American people could breathe a little easier.
Later, once the Soviets agreed to remove the ballistic missiles from Cuba, NSA reports also provided evidence to the American government that the Communist Bloc also considered the crisis over.
Looking back on the Cuban Missile Crisis, it is clear that SIGINT, combined with other types of intelligence such as photography and human sources, had pinpointed Cuba as a grave threat to the United States. The arms buildup and the defensive improvements spelled trouble, and focused the president and military leaders on the threat from Cuba long before the crisis erupted. In the middle of crisis, the intelligence system gave the president the information he needed to extricate the nation from its most dire crisis since the end of World War II.