What is the correct term used to indicate a unit is currently operational?

The term that indicates a unit is currently operational is "In service." This designation means that the unit is available and actively engaged in its duties, performing tasks as needed. When a unit is "in service," it is equipped, staffed, and ready to respond to calls or incidents.

In contrast, "Busy" could imply that the unit is engaged in a specific assignment but does not necessarily indicate its overall operational status, as it might still be able to take additional calls or not. "Out of service" clearly denotes that the unit is not available for operational duties, typically due to maintenance or other issues. "Relay" refers to a function where communication is transferred from one point to another, rather than a status of operational capacity. Thus, "In service" clearly and accurately reflects a unit's ability to perform its role effectively at any given time.