What is "chongtong"

The Chongtong was the name of most of the Korean gunnery used during the Joseon Dynasty. There were many different types, various improvements over the years, often including renaming. The well-known "Cheonja", "Jija", "Hyeonja", and "Hwangja" were named after the first four characters of the Thousand Character Classic in decreasing size, thus making them equivalent to Cannons A, B, C, and D.