S. Korean engineer figures out structure of Joseon Dynasty’s time bomb

During the Japanese Invasion of Korea, the army of the Joseon Dynasty struggled due to the Japanese soldiers’ use of matchlocks, but defeated them in other battles with advanced techniques using cannons and shells. The Jincheonroe, translated as heaven-shaking explosive shells, was one of the Joseon Dynasty’s secret weapons that scared the Japanese. However, the structure and characteristics of the time bombs launched from artillery guns had remained unknown as the manufacturing method was considered confidential and related records were lost.

Still, an engineer has revealed the structure and principle of the Jincheonroe for the first time. Chae Yeon-seok, a professor at the University of Science and Technology (UST), said Tuesday that the shell was a time bomb larger than a basketball with the weight of an adult male. As an expert in ancient firearms, Chae has studied ancient documents to do research on weapons like cannons and the Turtle Ship.

The Jincheonroe is a time bomb equipped with an ignition device, designed to explode in enemy camps. According to a book on military tactics regarding power weapons written in 1635 by Lee Seo, who served as the Minister of War during the reign of King Injo, the time bomb had a round iron body which weighs 67.8 kilograms, filled with three kilograms of gunpowder and 30 bracket-shaped caltrops. A fuse placed within a long structure was what controlled the time of explosion. When ignited, the fuse starts to smolder until it reaches powder and finally blows up. It is estimated that the debris of the body and caltrops would have gone off just like the way a grenade would explode.

What was the most difficult to figure out was the size of the Jincheonroe, as Chae could not find any records that show the exact size of the bomb. The researcher had to estimate the diameter of the bomb based on the book where it said the Jincheonroe was launched from the Large Mortar. The Large Mortar, called Daewangu, is one of the cannons used during the Joseon Dynasty and is known to have had the same size as that of the Chongtongwangu, a cannon invented in 1448 during the reign of King Sejong. There is a record that a shell which was 33 centimeters in diameter was launched from the Chongtongwangu. Based on this record, Chae assumed that the Jincheonroe would be 33 centimeters in diameter, about 1.4 times that of a basketball.

“During the Japanese Invasion of Korea, the soldiers of the Joseon Dynasty could defeat Japan using large guns of warships, the Turtiel Ship and the Panokseon, in naval battles, and mobilizing the explosive power of the Jincheonroe and the Bomb Shell in land combats,” Chae said.


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