What type of light is required on all motor vessels underway?

All motor vessels underway are required to display a masthead light or an all-around white light to ensure visibility and safety on the water. A masthead light is a white light that shines forward and is mounted at a height on the vessel, allowing it to be seen from a distance, particularly by approaching vessels. The all-around white light serves a similar purpose but can be visible from all directions. This requirement is based on navigational rules that aim to prevent collisions and promote safe passage, especially during low visibility conditions or at night.

Displaying the correct type of light is crucial for other vessels to recognize the nature of the vessel’s activity, helping them take appropriate actions to avoid potential accidents. In contrast, the other light options listed, such as red, blue, or flashing lights, do not fulfill the specific requirements for defining the operational status of a motor vessel underway and may actually signify different meanings in navigation or emergency situations.