What were the earliest Kongming lanterns used for?

Kongming lanterns are also called sky lanterns. According to legend, they were invented by Zhuge Kongming during the Three Kingdoms period. At that time, Zhuge Kongming was besieged by Sima Yi in Pingyang and was unable to send troops out of the city to ask for help. Kong Ming accurately calculated the direction of the wind, made a floating paper lantern, and attached a message for help. He was indeed out of danger, so later generations called this kind of lantern Kongming Lantern. Another theory is that the shape of this lantern is like the hat worn by Zhuge Kongming, hence its name.