"Surveillance of communications is often used as a means of gathering. How this is done is not talked about often. This is because the information that is acquired is often very good. Surveillance of enemy communications was one of the biggest factors in the American victory at Midway in 1942, and many other operations since. In 1943 Ten months later, a similar surveillance led to the mission in which Tom Lanphier shot down the plane carrying Isoroku Yamamoto. Communications intelligence also played a major part in defeating the U-boats in the Atlantic as well.

A lot of the methods used to gather intelligence in World War II (particularly codebreaking) were kept classified for decades after the Japanese surrender ended the war in 1945. Similarly, the Venona project stayed secret in the 1950s, even when information from that project could have defused controversies over the prosecution of the Rosenbergs or Alger Hiss.

In the war on terror, this is equally important. Not just for breaking up attacks, but also for mapping out the networks through a process known as traffic analysis. This can be done with just phone records (the leak of the NSA's request to various phone companies managed to tell terrorist which companies cooperated, and who company didn't). This is vital in terms of building an organizational chart of any enemy capabilities, but only if the enemy doesn't think that others are listening."