Repeating crossbow
A repeating crossbow (連弩) is one where the separate actions of stringing the bow, placing the bolt and firing it can be accomplished with a simple one-handed movement, all the while keeping the crossbow stationary. This allows the bow to fire at a faster rate compared to a normal crossbow. A box containing a number of bolts is present on top of the bow and the mechanism is worked by moving a rectangular lever forward and backward.
History
Repeating crossbows have a long history, with the oldest accurate written knowledge dating back to the Han dynasty (ca. 20-220 A.D.) in China. The Chinese repeating crossbow (诸葛弩, pinyin Zhū Gě nǔ, English transcription: Chu-ko-nu or Zhuge-nu, meaning 'Zhuge crossbow' in English) is an extremely simple piece of equipment. It is claimed to have been invented by Chinese strategist Zhuge Liang (181-234 A.D.), which is arguable since the earliest drawings of the weapon have been found from the buried library of Chu, dating all the way back to 250 B.C. It is more likely that during the Ming dynasty historians confused it with Zhuge Liang's invention of the lian-nu which shot two to three bolts at once and was used in massed formations. The Chinese repeating crossbow saw its last serious action in the China-Japan war of 1894-1895, where photographs show repeating crossbows as common weapons among Manchurian troops. The basic construction of this weapon has remained very much unchanged since its invention, making it one of the longest-lived mechanical weapons.
Chu-ko-nu (or Zhuge Nu)
The chu-ko-nu is one of the most simple, rugged and famous designs. This weapon was extremely easy to manufacture and use, and could easily launch ten arrows in fifteen seconds. In comparison, a standard arbalest could barely shoot one in that time. The chu-ko-nu, however, had neither the power nor accuracy of a common crossbow, for operational reasons. This gave it a shorter range, compensated for by using lightweight arrows instead of the heavy bolts of single-shot crossbows. Thus, the chu-ko-nu was not very useful against more heavily armored troops unless poison was smeared on arrows, in which case even a small wound could be fatal. Since a chu-ko-nu was shot from the hip, the accuracy was poor but could be adjusted very swiftly since the next shot was only a second away.
The chu-ko-nu was operated by moving a lever forwards and backwards. In that movement, a bolt would be dropped in place, the string would be strung, then the bolt would be shot and another one would be ready to take its place.
This put the weapon's string under heavy wear since it had forces straining it from above and below, and lifting of the magazine especially added serious pressure to the string. Nu-strings were therefore often reinforced with quills of birds, preferably swan or duck.
Alterations of chu-ko-nus included mountable siege crossbows with bigger arrows and greater power which required two men to operate: sighter and operator. There was also a heavy version using two magazines, thus doubling the number of arrows discharged. The latter was used in extreme close-quarter combat because they had extremely short range, and the bigger version which required two hands to operate was mounted on wall tops. They proved to be effective in defending gates and doorways of castles. It can be considered as a kind of submachine gun of the ancients.
It is noteworthy that the Hellenistic Greeks also had a repeating crossbow weapon which operated using a similar mechanism. Unlike the Chinese Zhuge Nu, the Greek repeating crossbow was a large weapon, shooting bolts that were a metre long. However, we are informed by the historian Dionysios of Halikarnassos that this weapon went out of fashion since the mechanism was too inaccurate - since it was a siege weapon there was little point in firing a round every second.
