(Pronounced: Bee-gyuck Jin-chunn-roy)
During the Imjin War (1592-1598), there was a legendary weapon that terrified the Japanese invaders. It was called ‘Vigeok-jincheon-roe’, which means “Heaven-Shaking Explosive Bolt.” As the name suggests, it flew through the air and exploded with a thunderous roar.
of the Joseon army
1. Advanced Science: The ‘Time-Delay Fuse’
What made this weapon truly terrifying was its adjustable explosion time, thanks to the ‘Mok-gok’ (Wooden Core) system.
- The Principle: Inside the bomb was a cylindrical wooden core with spiral grooves. A fuse was wrapped around these grooves. More wraps delayed the explosion; fewer wraps made it explode faster.
- Tactical Use: Soldiers adjusted the fuse length depending on the distance, allowing for precise detonation—a principle identical to modern hand grenades.
Internal Structure of Vigeok-jincheon-roe: A sophisticated time-delay fuse system using the ‘Mok-gok‘ (wooden core)
2. Lethal Shrapnel: The ‘Chul-jo’
The bomb wasn’t just filled with gunpowder. It contained dozens of sharp iron pieces called ‘Chul-jo’. Upon explosion, these shards scattered in all directions, neutralizing enemies within a radius of dozens of meters.
3. Success in Battle: The Siege of Gyeongju
The most famous use of this weapon was during the recapture of Gyeongju Fortress in 1592. The Japanese soldiers, unaware of the technology, gathered around the iron ball out of curiosity. Moments later, it exploded, causing chaos and allowing the Joseon army to retake the city.
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