What basic lights indicate a vessel is underway at night?

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

Answer: (B)

When a vessel is moving at night, you signal underway with a white stern light plus the two sidelights: a red light on the port (left) side and a green light on the starboard (right) side. The red and green sidelights show the vessel’s sides and help other mariners judge its direction and distance, while the white stern light confirms the vessel is making way and is visible from behind. This trio is the standard, basic set used to indicate a moving vessel at night. The option that lists the white stern light along with red port and green starboard sidelights matches exactly this combination, making it the correct choice. Other options mix in different lights or omit the necessary sidelights, which wouldn’t clearly indicate underway status.