The government's control of Goryeo was crumbling, and at the same time the pirates crossing the Korean Strait plundered much of the coastal regions.
Ch'oe sought to smuggle some examples of secret items, and eventually was able to obtain knowledge of the three key ingredients of gunpowder: sulfur, slack or fine coal, and potassium nitrate.
However, the process to obtain niter, the mineral form of potassium nitrate, was difficult, and he did not know how to prepare gunpowder from the raw materials.
After a chain of experimental failures, Ch'oe considered abandoning the project, but heard about a wealthy Chinese merchant named Li Yuan who had great knowledge of gunpowder.
The government gave him great support, establishing the official laboratory and factory for gunpowder in 1377; here Ch'oe invented various kinds of cannon and other firearms.