BOTH INTERNATIONAL & INLAND Which shall a vessel not under command display?

Correct Answer: Option D — two red lights at night and two black balls during daylight

Rule 27(a) requires a vessel not under command to exhibit two all-round red lights in a vertical line at night, or two black balls in a vertical line during daylight. This signal indicates the vessel is unable to maneuver as required by the Rules and is therefore unable to keep out of the way.