Which navigation-light configuration indicates a vessel is underway at night?

• A. Red port sidelight
• B. Green starboard sidelight only
• C. White stern light plus red port and green starboard sidelights
• D. White masthead light only

Answer: (C)

When a vessel is underway at night, it needs the standard navigation lights that communicate both presence and direction: red port sidelight, green starboard sidelight, and a white stern light. The red light on the left and the green light on the right sweep forward, showing other mariners which way you’re headed, while the white stern light points aft to indicate the vessel is making way. Having all three lights visible confirms the vessel is moving and under way. The other options don’t provide the full set: a single red or a single green light doesn’t indicate movement, and a white masthead light alone doesn’t show the required combination to signal underway status.