BOTH INTERNATIONAL & INLAND In a dense fog, you hear a whistle signal of one prolonged blast followed by three short blasts. This signal is sounded by a __________.

Under Inland Navigation Rules, for the condition where 'In a dense fog, you hear a whistle signal of one prolonged blast followed by three short blasts. This signal is sounded by a', the correct requirement is: 'manned vessel being towed'. This standard ensures clear navigational intent and collision avoidance.