Which of the following is essential for Link 11 communications?

Link 11 communications, also known as the Tactical Data Information Link (TADIL J), is designed for secure and reliable military communication among different forces. Secure radio communication is fundamental to Link 11 because it allows the exchange of tactical information in a protected manner, ensuring that sensitive military data is not intercepted by adversaries. This secure nature is crucial for maintaining operational security and for enabling real-time situational awareness among allied forces.

The other options, while relevant to various communication systems, do not specifically characterize the requirements of Link 11. Fiber optic cables and direct satellite links are associated with other communication technologies that may not be part of the Link 11 architecture. Non-secure phone lines are contrary to the requirements for Link 11 as these would compromise the confidentiality and integrity necessary for tactical operations. Therefore, secure radio communication stands out as the essential component for Link 11 communications.