In the 15th century, under the lead of Sejong the Great, who was himself a pioneer of scientific research, the performance of these heavy artillery improved dramatically. Having built a cannon range next to the Royal Court, and after much experimentation and study, King Sejong finally increased the extent of the cannons’ firepower from to . Naval cannons were also developed at this time and among them, Heaven, Earth, Black and Yellow cannon were later employed by Yi Sun-sin. The development of artillery steadily continued after King Sejong, and saw the invention of the "bigyeokjincholloe", a timed grenade that flung out hundreds of metal shards upon explosion, and the "dapoki", a machine capable of firing many arrows at once. One of the types of cannons were arrows with a pipe filled with gunpowder.