What does a vessel display to indicate she is not under command?

• A. One all-round red light
• B. Two red lights in a diagonal line
• C. Two all-round red lights in a vertical line
• D. A red flag

Answer: (C)

Not Under Command is shown when a vessel cannot keep out of the way of other vessels, usually due to a loss of maneuverability. To warn others, she displays two all-round red lights in a vertical line, visible from all directions, while underway. This clear, vertically aligned pair of red lights signals that the vessel cannot maneuver to avoid a collision, so other vessels should take early and substantial action to stay clear. In daylight, the same situation is indicated by two black balls in a vertical line as a day shape.

The other signals do not meet the standard indication for Not Under Command: a single red light isn’t the required signal; a red flag isn’t the correct day or night indication; and two red lights in a diagonal line do not match the mandated vertical arrangement.