Question 39 RVR02 - Master of LT 500-1600 GRT

The Correct Answer is D **Explanation for Option D (law enforcement vessels):** Option D is correct because, under the U.S. Inland Navigation Rules (specifically Rule 21(d)), a flashing blue light is used exclusively to identify vessels engaged in law enforcement services. This light may only be displayed when the vessel is actively engaged in direct law enforcement or public safety duties. This provision is unique to the Inland Rules and does not apply to international waters (COLREGs). **Explanation of Why Other Options Are Incorrect:** * **A) dredge pipelines on trestles:** Dredge pipelines, especially if they obstruct a navigable channel, are marked with fixed yellow or white lights to show their location, not flashing blue lights. * **B) air-cushion vessels in the non-displacement mode:** Air-cushion vessels (hovercraft) operating in the non-displacement mode (on cushion) are required to display a high-intensity **flashing yellow** light, not a flashing blue light, as an identification signal. * **C) U.S. submarines:** U.S. submarines, when surfaced, display standard navigation lights. While they may use special warning lights (often flashing amber or high-intensity white) during operations, the flashing blue light is not the regulatory signal for identification of submarines.