What lights indicate a vessel is underway at night?

• A. Sidelights (red on the port side, green on the starboard side) and a white stern light; if not underway, an anchor light may be shown.
• B. No lights.
• C. Only a white light.
• D. Red light on the port side.

Answer: (A)

When a vessel is moving at night, you’ll see a specific combination of lights that signals motion and helps others judge your direction. The red light on the port side and the green light on the starboard side (the sidelights) together with a white light at the stern show you are underway. The sidelights tell other mariners which way you’re moving, while the white stern light confirms you’re proceeding and where you’re headed from behind. An anchor light is used only when the vessel is not underway, to indicate it’s at anchor. A single white light or red light alone doesn’t convey that you’re underway, so the full set of sidelights plus stern light is the correct indication.