The hwacha was an anti-personnel weapon developed by the Koreans, and it is believed to have been one of the first gunpowder-based anti-personnel weapons ever created. The hwacha was a platform constructed to launch large numbers of fire arrows (or "Shin Ki Chon") at enemy targets. Hwachas were mounted on carts and wheelbarrows. A typical hwacha platform held seven or more rows of fifteen arrows and could fire from 150 to 200 fire arrows at once. The fire arrows had hollow tips and the shafts were fitted with narrow pipes. The tips and pipes were filled with gunpowder and each was equipped with a fuse.
When lit, the fire arrows' fuses would first ignite the powder in the pipes, causing the arrows to shoot off like rockets. The fuses would continue to burn until they reached the gunpowder in the arrows' heads, which would then explode - with luck, somewhere near enemy soldiers. However, the weapons were extremely inaccurate and the Koreans had to fire off huge volleys to ensure significant damage to their targets.
The Shin Ki Chon fire arrows were first developed in Korea and China around 1400 AD, and the hwacha dates from shortly after this period. The fire arrows could travel as far as one kilometer, an amazing range for artillery weapons at that time. Given their famous inaccuracy, the hwacha was best used against massed enemy formations at medium range: even if not precisely on target when they exploded, shrapnel from the fire arrows could still significantly hurt the enemy. Hwacha also were useful shock weapons, due to the noise and light produced by the rocket-like exploding arrows, and even seasoned troops could break and run the first time they encountered the strange new weapon.
The best-known use of hwacha historically was during the Japanese invasion of Korea in 1592-98. The Japanese samurai typically advanced in dense groups - easy targets for the hwacha. At the Battle of Haengju, 3400 Koreans were able to defeat 30,000 Japanese with the help of 40 hwacha.
The hwacha eventually became obsolete when more efficient metal projectiles (like bullets and artillery shells) replaced the fire arrows.