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

Correct Answer: Option D — A vessel being towed

Rule 35(c) identifies that a vessel not under command, restricted in her ability to maneuver, engaged in fishing, or towing, must sound one prolonged followed by two short blasts. A vessel being towed is excluded from this list, as it must sound one prolonged followed by three short blasts.