Which of the following best describes the responsibilities of the Command Duty Officer during a security alert?

The responsibilities of the Command Duty Officer during a security alert are primarily focused on securing the ship from conditions of threat. This role is critical as it encompasses not only the immediate tactical response to potential security breaches but also the overall safety and security posture of the vessel. The Command Duty Officer directs security measures, coordinates with other officers and crew members, and ensures that protocols are followed to mitigate any identified threats.

In contrast to other options, handling personnel matters is typically the domain of human resources or other dedicated personnel, not the Command Duty Officer in a security context. Commanding a naval fleet is a strategic and broader responsibility that goes beyond the scope of individual ship duty, and judging crew efficiency does not directly pertain to the immediate actions required during a security alert. Thus, the focus is clearly on the proactive and reactive measures necessary to protect the vessel, which is why the correct choice centers on the responsibility of securing the ship from threats.