What procedures must be followed when a secure communications line cannot be established?

When secure communications lines cannot be established, the combination of COMSEC (Communications Security) and OPSEC (Operational Security) procedures becomes paramount. COMSEC involves the protection of communications and ensuring that information being transmitted is safeguarded against unauthorized access and interception. When secure lines are compromised or unavailable, ensuring the confidentiality and integrity of communications is critical.

In conjunction with COMSEC, OPSEC plays an essential role in safeguarding operations by identifying and protecting sensitive information that might be vulnerable to adversaries. OPSEC includes various practices to prevent the unintentional disclosure of critical operation details that could be exploited, particularly when secure lines aren't an option. By applying both COMSEC and OPSEC procedures, personnel can mitigate risks associated with unsecured communications and protect sensitive information effectively.

While the other options reference security concepts, they either focus on different aspects or lack the critical intersection of operational security with communications security necessary in scenarios where secure methods fail.