What action is required of a vessel when a collision is imminent?

Answer: A — Change course and speed as needed

When a collision is imminent, the appropriate action for a vessel is to change course and speed as needed to avoid the situation. This response aligns with the principles laid out in the COLREGs, specifically the need to take immediate and effective measures to prevent a collision. By altering course and speed, the vessel can create a more favorable situation to navigate away from the path of another vessel, adapting to the circumstances in real-time. This proactive approach helps ensure that the navigator is taking responsibility for avoiding a collision, which is vital in maintaining safety at sea. Other options do not reflect the necessary urgency of the situation. For instance, maintaining speed and course could lead to an unavoidable collision. Significantly reducing speed might not provide enough time for a vessel to change its position effectively. Sounding the horn continuously, while it can be a signal of danger, does not contribute to avoiding the collision itself and could lead to confusion or alarm without taking action to alter the vessel's trajectory. Therefore, actively changing course and speed is the best practice in such scenarios.