What additional light must be displayed by an air cushion vessel in non-displacement mode?

An air cushion vessel operating in non-displacement mode must display an all-round flashing yellow light to signify its status and to ensure its visibility to other vessels. This requirement is specific to air-cushion vessels to help avoid collisions and to communicate their unique maneuverability characteristics. The all-round flashing yellow light serves as a warning, indicating that the vessel may not be operating like a traditional ship, which is crucial for maintaining situational awareness among nearby vessels.

In the context of maritime safety, the use of certain colored lights is governed by the COLREGs, which establishes the guidelines for navigating vessels safely. The yellow light serves a clear purpose by aiding other mariners in recognizing the presence of an air cushion vessel and allows them to make informed decisions regarding their own navigation around it.

While the other options listed represent different light signals that may be used by various types of vessels in specific situations, they do not apply to air cushion vessels in non-displacement mode according to the COLREGs criteria. Therefore, the requirement for an all-round flashing yellow light is essential for ensuring proper recognition and safety on the water.