A "head on" situation shall be deemed to exist at night when a power driven vessel sees another power-driven vessel ahead and __________.

In a "head on" situation, the definition of visibility between two power-driven vessels is crucial for determining the appropriate actions to avoid a collision. At night, if a vessel observes both sidelights and the masthead light of another power-driven vessel, it indicates that the two vessels are approaching each other directly. This visibility confirms that the vessels are on a collision course since the sidelights are characteristic of a vessel's port and starboard sides being illuminated, while the masthead light is positioned at the front.

The sighting of both sidelights alongside the masthead light means the vessel observing the lights is positioned directly in front of, or very nearly in front of the other vessel, and this is a key indicator for setting protocols for safe navigation. When this scenario occurs, the vessels must alter their courses to avoid a collision, as outlined in navigation rules.

Visibility of only one sidelight or the masthead light alone does not sufficiently indicate a "head on" situation, as it could mean the vessels are not crossing each other's path directly, which is why other options do not support the definition of a "head on" encounter. The presence of both sidelights along with the masthead light signals a clear risk of collision, requiring immediate navigational