Which of the following is a required action for maintaining Link 16 network operations?

Net number selection is a crucial action for maintaining Link 16 network operations because it establishes the unique network identity for each participating node in the system. This selection determines how devices communicate within the network and facilitates the allocation of resources and bandwidth. Each net number corresponds to a specific data link and enables interoperability among various platforms and units, ensuring effective synchronization of operations.

While other options, such as data transmission encoding, encryption key updates, and system diagnostic checks, are integral to the entire operational framework, net number selection specifically addresses the foundational aspect of network connectivity and participant identification within the Link 16 system. This is essential for ensuring that all systems involved can effectively send and receive traffic without conflict or data loss.