BOTH INTERNATIONAL & INLAND While underway in fog, you hear a signal of one prolonged blast followed by three short blasts. This is the fog signal for a vessel __________.

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