Volley fire, as a military tactic, is (in its simplest form) the concept of having soldiers shoot in the same direction en masse. In practice, it often consists of having a line of soldiers all discharge their weapons simultaneously at the enemy forces on command, known as "firing a volley", followed by more lines of soldiers repeating the same maneuver in turns. This is usually to compensate for the inaccuracy, slow rate of fire (as many early ranged weapons took a long time and much effort to reload), limited effective range and stopping power of individual weapons, which often requires a massed saturation attack to be effective. The volley fire, specifically the musketry volley technique (also known as the countermarch), requires lines of soldiers to step to the front, fire on command and then march back into a column to reload, while the next row repeats the same process.
The term "volley" came from Middle French , substantivation of the verb , which in turns came from Latin , both meaning "to fly", referring to the pre-firearm practice of archers mass-shooting into the air to shower their enemy with arrows. While the tactic of volley fire is usually associated with Dutch military thinkers in the late 16th century, its principles have been applied to crossbow infantry since at least the Chinese Tang dynasty.
History
Crossbows
Although volley fire is most often associated with firearms, the concept of continuous and concerted rotating fire may have been practiced using crossbows since at least the Han dynasty as described in the Han-Xiongnu Wars in the Records of the Grand Historian, although it was not until the Tang dynasty that detailed illustrations appeared. During the An Lushan Rebellion the Tang general Li Guangbi successfully deployed a spear crossbow formation against the rebel cavalry forces under Shi Siming. In 756 Shi Siming raced ahead of the main army with his mounted troops to intercept Li Guangbi's Shuofang army near the town of Changshan. Li took Changshan in advance and set up his men with their backs to the town walls to prevent a sneak attack. The spearmen formed a dense defensive formation while 1,000 crossbowmen divided into four sections to provide continuous volley fire. When Shi's cavalry engaged Li's Shuofang army they were completely unable to close in on his troops and suffered heavy losses, forcing a withdrawal.
The 759 AD text, Tai bai yin jing (太白陰經) by Tang military official Li Quan (李筌), contains the oldest known depiction and description of the volley fire technique. The illustration shows a rectangular crossbow formation with each circle representing one man. In the front is a line labeled "shooting crossbows" (發弩) and behind that line are rows of crossbowmen, two facing right and two facing left, and they are labeled "loading crossbows" (張弩). The commander (大將軍) is situated in the middle of the formation and to his right and left are vertical rows of drummers (鼓) who coordinate the firing and reloading procedure in procession: who loaded their weapons, stepped forward to the outer ranks, shot, and then retired to reload. According to Li Quan, "the classics say that the crossbow is fury. It is said that its noise is so powerful that it sounds like fury, and that's why they named it this way," and by using the volley fire method there is no end to the sound and fury, and the enemy is unable to approach. Here he is referring to the word for "crossbow" nu which is also a homophone for the word for fury, nu.
The encyclopedic text known as the Tongdian by Du You from 801 AD also provides a description of the volley fire technique: "[Crossbow units] should be divided into teams that can concentrate their arrow shooting.… Those in the center of the formations should load [their bows] while those on the outside of the formations should shoot. They take turns, revolving and returning, so that once they've loaded they exit [i.e., proceed to the outer ranks] and once they've shot they enter [i.e., go within the formations]. In this way, the sound of the crossbow will not cease and the enemy will not harm us."