Final answer:
Vessels less than 65.6 feet in length are required to carry a whistle or horn, or some other means to make a sound signal for safety purposes.
Step-by-step explanation:
The question of what are vessels less than 65.6 feet in length required to carry pertains specifically to boating safety requirements. Vessels of this size are generally required to have onboard a whistle or horn or other means to make a sound signal.
While the excerpt provided references various maritime visuals like flags, fires, and the colors of nations, these are not requirements for smaller vessels.
The primary requirement from the options listed is the need for a sound-making device to signal one's presence to other boaters to prevent collisions or alert in case of emergency.