What is the primary purpose of the "Substitute" flags in naval communication?

The primary purpose of the "Substitute" flags in naval communication is to represent missing personnel or officers. These flags serve as a visual means of conveying important information regarding the status of certain individuals within a naval unit. When a ship or command needs to indicate that a specified officer or key personnel are unavailable, using a Substitute flag effectively communicates this situation to other vessels or commands. This is crucial in maintaining operational status and ensuring proper command and communication flow within a fleet.

The other choices, while relevant to naval operations, do not pertain to the specific function of Substitute flags in naval communication. Distress signals are addressed through different flag signals designed for emergencies, operational readiness indicators relate to broader assessments of a vessel's ability to undertake missions, and organizing naval exercises involves separate planning signals. The unique role of Substitute flags is specifically tied to personnel status within maritime communication protocols.