BOTH INTERNATIONAL & INLAND While underway in fog you hear a whistle signal consisting of one prolonged blast followed immediately by two short blasts. Which vessels are required to sound this signal in fog?

Correct Answer: Option D — Vessels underway and towing

Rule 35(c) explicitly mandates that a vessel engaged in towing or pushing another vessel shall sound one prolonged blast followed by two short blasts at intervals of not more than two minutes. This signal is essential for alerting other traffic to the presence of a tow in restricted visibility.