The repeating crossbow (Chinese: 諸葛弩; pinyin: Zhūgě nǔ; Wade–Giles: Chu-ke nu; literally: "Zhuge crossbow"; sometimes romanized as Chu-ko-nu), also known as the lián nǔ (simplified Chinese: 连弩; traditional Chinese: 連弩; literally: "continuous crossbow") or Nỏ Thần (in Vietnamese), is a crossbow where the separate actions of stringing the bow, placing the bolt and shooting it can be accomplished with a simple one-handed movement while keeping the crossbow stationary. This allows a higher rate of fire than a normal crossbow: there is a magazine containing a number of bolts on top of the bow, and the mechanism is worked by moving a rectangular lever forward and backward.
The repeating crossbow has a very simple and rugged design. The basic construction of the weapon has remained very much unchanged since its invention, making it one of the longest-lived mechanical weapons. The bolts of one magazine are fired and reloaded by simply pushing and pulling the lever back and forth. In that one movement, a bolt would be dropped into place, the string tensioned, and then the bolt released. Another bolt would then be ready to take its place from the magazine above. This action however put the weapon's string under heavy wear since it had forces straining it from both above and below. The lifting of the magazine especially, put severe pressure on the string. The bow string consists of animal sinew twisted into a cord of suitable strength, often reinforced with quills from bird feathers, preferably those from swans or ducks.
The weapon used by the ancient militaries was developed into a composite-recurve variety for more power. The recurved repeating crossbow is generally still weaker than the regular recurved crossbow, and was mainly used for sieges or behind shield cover. The Chinese repeating crossbow had a maximum range of 120 meters, with an effective range of 80 metres (260 ft). Non-recurved versions of the repeating crossbow were often used for home defense.
The weapon was extremely easy to manufacture and use, and, in the hands of a trained soldier, could easily launch ten bolts in fifteen seconds. In comparison, an arbalest could only deliver about two bolts a minute. The repeating crossbow, with its smaller and lighter ammunition, had neither the power nor the accuracy of an arbalest, however. Thus, it was not very useful against more heavily armoured troops unless poison was smeared on bolts, in which case even a small wound may prove fatal. Since the repeating crossbow was shot from the hip, accuracy was poor, but the aim could be adjusted very swiftly since the next shot was only a second or two away. To get past these limits often large numbers of men would use it on the battlefield, allowing for large numbers of bolts to be fired.
Archaeological evidence of the earliest repeating crossbow from Tomb 47 at Qinjiazui, Hubei Province has been dated to the 4th century BC, during the Spring and Autumn period. However, its invention is commonly attributed to Zhuge Liang (181–234 AD), a famous military advisor of the Three Kingdoms period; Zhuge Liang improved the design of the repeating crossbow, and made a version which shot two to three bolts at once and was used in massed formations. For this reason, it was named after him. Other repeating crossbows fired as many as 10 bolts before exhausting the magazine.
The repeating crossbow was introduced into Korea by King Sejong (1418–1450), who during a trip to China saw the weapon and was impressed by its mechanism. In Korean it was called sunogung (Hangul: 수노궁; hanja: 手弩弓).
Alterations of the design included mountable siege crossbows with larger bolts and greater power which required two men to operate (a spotter and bowman). There was also a heavy version using two magazines, thus doubling the number of bolts discharged. The latter was used in extreme close-quarter combat because they had extremely short range, due to the power of the bowstring being split between the two projectiles. A larger version that required two hands to operate was sometimes mounted on top of castle walls. They proved to be effective in defending the gates and doorways of castles.
- Gallwey, Sir Ralph (1990). "The Crossbow" (Ninth Impression ed.). The Holland Press. p. 337.
- Lin, Yun. "History of the Crossbow," in Chinese Classics & Culture, 1993, No.4: p. 33–37.
- "Chu-Ko-Nu: The Manchurian Repeating Crossbow". 22 June 1995.
- "쇠뇌 1.수노궁". 조선의 무기와 갑옷 (in Korean). 2004. p. 98. ISBN 89-8435-207-1.