Why did intelligence agencies tap communications lines during the Cold War?

During the Cold War, intelligence agencies tapped communication lines as a primary method of signals intelligence (SIGINT) to gain critical strategic advantages. By intercepting and analyzing foreign electrical communications, agencies could gain unauthorized access to an adversary's internal strategies, military weaknesses, and shifting attitudes.12

This practice was essential because it allowed nations to "read the mind" of opposing high commands, much like the successful Ultra project during World War II. In the context of military science, such intelligence is highly valued because it provides decision-makers with advance knowledge of enemy movements and capabilities, which can be decisive in both offensive and defensive operations. During the latter part of the Cold War, the United States specifically relied on these technical means to monitor Soviet weapons of mass destruction.21

While intelligence gathering is a standard function of state security, it is important to acknowledge that such activities—often involving the covert surveillance of communications—are frequently viewed as ethically complex, balancing the necessity of national defense against the fundamental principles of privacy and international conduct.2