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A hwacha model at the Seoul War Memorial.
Hwacha or Hwach'a (화차; 火車) (fire cart) was a multiple rocket launcher developed and used in Korea during the Joseon Dynasty (1392–1897). It had the ability to fire up to 200 Singijeon, a type of fire arrow rocket, at one time. The hwacha consisted of a two-wheeled cart carrying a board filled with holes into which the singijeon were inserted.
Some East Asian historians believe this technological breakthrough, alongside the turtle ship in the mid-16th century, had a distinctive effect during the Imjin War. Today, hwacha appear in Korean museums, national parks, and popular culture.
Long before the development of the hwacha, China imposed severe restrictions on exporting gunpowder to Korea, fiercely guarding a military asset. Yet, gunpowder weapons were key to the Koreans in maintaining a predominant navy in the Sea of Japan (East Sea) to protect fishermen and merchants against the increasing numbers of invading Japanese and Wokou pirates.
In response, there was an effort by Koreans to develop gunpowder on their own. Between the years of 1374 to 1376, Korea began its first productions of gunpowder. In 1377 a Korean scholar named Choe Mu-seon, discovered a way to obtain gunpowder by extracting potassium nitrate from the soil and subsequently invented the Juhwa, Korea's very first rocket. Further developments led to the birth of the family of singijeons.
The hwacha was a brainchild of its predecessors, the Juhwa and the Singijeon. The first hwacha was develeoped in Korea in 1409 during the Joseon Dynasty by several Korean scientists, including Yi Do (이도) and Choi Hae-san (최해산).
During the rule of Sejong the Great, hwachas were further developed and extensively made. Records show that during this time 90 hwachas were in use. King Sejong, famous for his contribution to Hangul, made efforts to improve the hwacha and by the end of his rule a single hwacha could fire 200 rocket arrows at one time.
Stronger and more effective hwachas were made in 1451 under the decree of King Munjong. At the time, 50 units were deployed in Hanseong (present-day Seoul), and another 80 on the northern border. By the end of 1451, hundreds of hwachas were deployed throughout the peninsula.
Imjin wars (1592–1598) 
Hwachas saw action most extensively during the Japanese invasions of Korea against the Japanese soldiers. They were mostly placed in fortresses or citadels, and used in defensive manner. These proved to be powerful in many battles, and were most prominent in the Battle of Haengju, in which 3,400 Koreans repelled 30,000 Japanese with the help of 40 hwachas. The Japanese samurai infantry, especially in the Battle of Haengju, typically advanced in dense formations, presenting ideal targets for the hwacha.
The hwacha's structure was very similar to a hand cart with a mobile wooden launchpad on the top filled with 100 to 200 cylindrical holes, into which the ignitors like sajeonchongtong (사전총통) were placed.
The ammunition, similar to the Chinese fire arrow, consisted of a 1.1 m long arrow with the addition of a paper tube filled with gunpowder attached to the shaft just below the head. Approximately 100 projectiles were loaded and launched in one volley, and had a range up to 2000 meters.
One variant had 5 rows of 10 gun barrels in the launchpad, each of which could fire a bundle of four arrow-like projectiles.
The back side of the hwacha featured two parallel arms that allowed the operator to push and pull the machine, and a vertical strip designed for in-line attacks or stand ground-sentry positions.
Hwachas were usually made of pine wood, although there are some versions made of oak. Ropes used within were usually made of hemp.
The Korean army included siege engineers and blacksmiths in order to make repairs to the Hwacha if poor road conditions, bad weather, or battle damaged the machinery.
Unlike cannons or mortars used in Western warfare during the 16th century and the Middle Ages, which required heavy iron balls, Hwacha fired arrows which were thin and light, making it an easy-to-maneuver siege weapon.
The holes in the top of the launching pad in Hwacha ranged in diameter from an inch to an inch and a half, which allowed thin Gungdo bow-like arrows to be fired and also admit sajeonchongtong class ignitor to be placed in the back side of the shooting board.
Singijeon-class projectiles were small arrows designed by Korean siege engineers specifically to be used in Hwacha. Called (so) (소) they possessed a pouch of black powder attached in the bottom near to the fletching section. Besides the singijeon-class projectiles, hwacha could also fire 100 steel-tipped rockets.
Because of the large numbers of arrows fired from Hwachas and the wide spread damage of its attack, a dense formation presented an ideal target for Hwachas.
Ballistics and range 
The trajectory of the so (소; "small") size singijeon projectiles was fairly flat and – like other spinning projectiles – experienced the Magnus effect. Operators used to fire the weapon with an angle nearly 45 degrees to maximise range. Adverse weather conditions (wind, humidity, rain) during a battle generally limited their striking distance to about 100 meters.
Hwachas' range could be extended if the siege weapon was situated in elevated places like hills. Singijeon arrows from that position had a range of about 500 yards (≈450 meters).
A 15th century account from the Annals of Joseon Dynasty tells us of an experiment, in which the Singijeon fired from the Hwacha completely pierced a scarecrow armed with a suit of armour and shield, at the range of 80 paces (about 100 metres).
Hwachas were mostly used in defensive manners; however, some Western and East Asian historians have recently concluded that in some cases they had been used offensively in sea to surface attacks and in naval warfare as well, particularly in the Battle of Noryang Point, during the Imjin wars in 1598.
Hwachas were usually carried to battle highly escorted. Once the army settled down in trenches or base camps, the operators would disassemble the siege weapon by placing the launching pad on the top. Transporting Hwachas were similar to European trebuchets and required assembling before usage. All the pieces featured similar characteristics and the mobile launching pad could be unpacked and easily placed on the wood outlet on the top of cart.
Once a hwacha was set up for combat, the operators would use the gunpowder stored on a boot-like bag tied on each ignitor to be used for each hole on the machine. After that, the operators were able to load the Hwacha with arrows or iron spikes and be ready for shooting. To do so, the operators stepped back and covered their ears, pulling the ropes that contained each ignitor thus blasting fire on its opponent.
At sea, maneuvers were slightly different and complex because the operator would need to find a proper and stable place to fire. Usually some Hwacha operators preferred to be in the rowers deck where they were able to shoot from the windows, while others preferred to be in the main deck so they could shoot to the sails of the enemy ships. This kind of maneuvers was particularly seen in Korean Panokseon warships.
See also 
- Japanese invasions of Korea (1592-1598)
- Fire arrow
- MythBusters (2008 season)#Hwacha
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