BOTH INTERNATIONAL & INLAND While underway in a fog, you hear a whistle signal of one prolonged blast followed by two short blasts. This signal could mean all of the following EXCEPT a vessel __________.

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