We think of rocket launchers as a modern invention, but the Koreans were using them four hundred years ago. The hwacha could fire two hundred rockets at once, blowing up enemies more than a hundred metres away.
The hwacha were made of wood and mounted on two wheels like a cart, so they could be manoeuvred and positioned quickly. They fired a volley of fire arrows (a light wooden projectile) that exploded on impact.
One contemporary account suggests they could pierce a full suit of armour. The Koreans certainly used them to great effect against the Japanese in the Imjin Wars, devastating the samurai infantry at the Battle of Haengju. Only 2300 men held off a force of 30,000 with the help of 40 hwacha.