Question 39

The Correct Answer is D **Explanation for Option D (law enforcement vessels):** The use of a flashing blue light is specifically regulated by the Inland Navigational Rules (33 CFR Subchapter E). Rule 21(d) of the Inland Rules, concerning color specification, states: "A flashing blue light is a light which flashes at regular intervals at a frequency of 50 to 70 flashes per minute and is reserved for use by law enforcement vessels when engaged in enforcement duties and must be placed so as not to interfere with the visibility of the vessel's navigation lights." Therefore, a flashing blue light is used exclusively to identify law enforcement vessels while they are performing their official duties on U.S. Inland Waters. **Explanation for Incorrect Options:** * **A) dredge pipelines on trestles:** Dredge pipelines, especially those that are fixed or semi-fixed, are generally marked by fixed or flashing **yellow** lights (or white lights if not obstructing a channel), or by day shapes, but not specifically by a flashing blue light. * **B) air-cushion vessels in the non-displacement mode:** Air-cushion vessels (like hovercraft) operating in the non-displacement mode (flying/hovering) must exhibit an all-round flashing **yellow** light (Rule 23(b)(4)), not a blue light, to signify that they are restricted in maneuverability due to their operational status. * **C) U.S. submarines:** U.S. submarines are military vessels. While they may use special lights or signals when operating on the surface, they do not use a standard flashing blue light reserved for law enforcement. Submarines often use an intermittent flashing **amber/yellow** light when proceeding on the surface, as required by the International Rules (and often adopted by the Navy), but not the flashing blue light reserved for Inland law enforcement.