BOTH INTERNATIONAL & INLAND While underway in fog, you hear a signal of one prolonged blast followed by three short blasts. Which vessel shall sound this fog signal?

Correct Answer: Option C — A manned vessel being towed

COLREGS Rule 35(c) requires a vessel being towed, if manned, to sound one prolonged followed by three short blasts at intervals of not more than two minutes. This signal is sounded immediately after the signal made by the towing vessel to indicate the presence of the tow.