BOTH INTERNATIONAL & INLAND You are underway, in fog, when you hear a whistle signal of one prolonged blast followed by two short blasts. This signal could indicate which type of vessel?

Correct Answer: Option A — Not under command

Rule 35(c) requires a vessel not under command to sound one prolonged blast followed by two short blasts at intervals of not more than two minutes. This signal identifies the vessel's inability to maneuver as required by the Rules, distinguishing it from other vessels in restricted visibility.