INTERNATIONAL ONLY Vessels "A" and "B" are meeting on a river as shown in illustration D041RR below and will pass 1/4 mile apart. If you are on vessel "A", in addition to the sidelight, which other light(s) will you see on vessel "B"?

Correct Answer: Option C — Two white masthead lights in a vertical line

Rule 23(a) requires a power-driven vessel underway to exhibit a masthead light forward and a second masthead light abaft of and higher than the forward one. These two white lights in a vertical line are the standard configuration for a power-driven vessel underway on the high seas.