BOTH INTERNATIONAL & INLAND You see a red sidelight bearing NW (315°). That vessel may be heading __________.

Correct Answer: Option B — south (180°)

When a vessel bears NW (315°) from your position and displays a red sidelight, it is showing its port side to you. Tracing the geometry under COLREGS sidelight visibility sectors, a vessel heading south (180°) will present its red port light to a northwest observer.