Han Dynasty Crossbow III

HackneyedScribe

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Feb 2011
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The following is a rehash of Han Dynasty Crossbow thread. The reason I reproduced this again is because the forum re-design converted a lot of characters in that thread into random gibberish, making things hard to read. So I made this thread and I added additional new information that wasn’t available to me back then.


Han Dynasty Crossbow Technology

The prevalence and praise of the crossbow in ancient Chinese texts is so widespread (The excavated Donghai accounting records show the existence of up to half a million crossbows in its stockpile) that I find this single weapon notable enough to write an entire article centered on it. No doubt, from its inception during the 6th century BC the crossbow revolutionized Chinese warfare. Projectiles fired from a crossbow are much more powerful than those fired from bows, and only a little time is needed for one to become proficient with it. Bolts can be fired with enough force to penetrate shields and armor at a distance. No longer can heavily armored, skilled nobility outmatch the everyday peasant. This essay only deals with ancient crossbows of the Han dynasty, although it was one of the primary weapons in Chinese history for a much longer time than the dynasty itself.

Range and Draw Weight
Just how powerful a crossbow could be is glimpsed in the excavated Chu-yen slips, from which records of crossbow maintenance was kept. In general crossbows were categoized by draw weight of 1, 3, 4, 5, 6, 7, 8, and 10+ stone, with each stone unit being the modern equivalent of ~64.5 pounds. The majority of crossbows have a draw weight of 6 stone. The following is a calculation on the percentage of crossbows for each categorical draw weight, but it is currently not verified by me as I did not count them personally (However, historian Yang Hong also states that the majority of crossbows were categorized with draw weights of 6 stone):

1 stone: 1.37%
2 stone: 1.37%
3 stone: 21.92%
4 stone: 2.74%
5 dan: 17.81%
6 dan: 43.84%
7 dan: 2.74%
8 stone: 2.74%
10 stone and above (Great Yellow Crossbow): 5.48%

From the slips already excavated, we have a set of records showing six crossbows shooting 168 to 280+ meters. Each of these crossbows only had draw weights of 3-5 stone, as compared to typical Han era crossbows of 6 stone. Two slips record tests for their penetration ability. Both tests show that the crossbows punctured a wooden wall (most likely a plank or fence) at 252 meters.

Slip 14.026: 一今力五石廿九斤射百八十步辟木郭
Translation: Present strength 5 stone 29 jin (341 lbs) and will penetrate a wooden wall at 180 paces (252 meters).
Slip 515.46: 三石具弩射百廿步
Translation: 3 stone (193.5 lbs) crossbow, fully assembled, shoots 120 paces (168 meters)
Slip 36.10: 官第一六石具弩一今力四石【四十】二斤射白八十五步完
The words in【】is used to display what the word on the slip means, but the actual word cannot be typed by computer as the word is no longer in use)
Translation: Number one 6 stone crossbow, fully assembled, present strength is 4 stone 42 chin (285 lbs), and it will shoot to the end of 185 paces (259 meters).
Slip 510.026: 五石具弩射百廿步
Translation: Five stone crossbow fully assembled, shoots 120 paces (168 meters)
Slip 341.3: 具弩一今力四石射二百…(too smeared to make out)…
Translation: Fully assembled crossbow, present strength 4 stone (258 lbs), shoots two hundred and [text too smeared to make out] (280-418.6 meters).
Slip 14.62A: 一今力三石廿九斤射百八十步辟木郭
Translation: Present strength 3 stone 29 jin (212.2 lbs) and penetrates wooden wall at 252 meters.


Thankfully, the weight Han crossbows projectiles scaled linearly with their draw weight (15.625 grams per lb). This can be seen in the WuYue ChunQiu:

夫射之道,從分望敵,合以參連。弩有斗石,矢有轻重,石取一两,其数乃平,远近高下,求之铢分。道要在斯,无有遗言。​
Translation:The rule in all archery is: let your eye follow the calibrated line of fire from you to the target, then line up the three elements (calibration, arrowhead and target). The power of crossbows is measured in heavy or light poundage; arrows differ in their weights. The ratio of arrow weight to bow poundage is one liang to one stone: this gives you the correct proportion. Different distances and elevations can be compensated by minute differences in this weight. This is the whole method: I have held nothing back.

Combined with the range, we can derive a rough minimum estimate of the energy and velocity of the projectile when shot:


The only crossbow in the list that represent the common six stone crossbow had decreased in draw weight from 387 lbs to 285 lbs at the time it was shot. Crossbow replica maker Andreas Bichler mentioned how composite prods could decrease in draw weight over time in hot/humid environments, while gaining the draw weight back when the season became dry/cold. This was the most likely explanation for the decrease in draw weight that was mentioned for some crossbows in the Chu-yen slips. To top this off, the Song dynasty manual Cui Wei Xian Sheng Bei Zheng Lu did mention that composite prods of crossbows should be replaced by a wooden prod during the wet summer, only to be put back on again during the dry winter:

During the hot summer, when it’s raining and there’s steam, the horn [composite prod] should be easily taken off, and use a wooden [simple prod] crossbow. During the spring and winter, where there is wind and bitter cold, the wood (simple prod) is heavy and sluggish, and horn [composite prod] crossbows must be used.

Nevertheless, even a reduced six stone crossbow of merely 285 pounds managed to shoot 259 meters. Using the typical 93.75 gram projectile designed for such a crossbow, the joules of energy for the projectile was impressive at roughly 195 joules. If the crossbow shot with its full draw weight, the amount of joules for the projectile would go significantly above 200 joules, especially when considering that the weight of the crossbow prod would not have increased in mass. This was because the decrease in draw weight was not caused by reducing the mass of the prod, but most likely because the weather caused the glue to start breaking apart, decreasing prod stiffness. Reversing the logic, a Han crossbow with an original draw weight of 285 lbs (rather than an originally 387 lb crossbow with its draw weight decreased to 285 lbs) would also shoot further and harder due to lighter prod mass.

The reader can compare this with the 150 lb longbow shots mentioned in the book “The Great Warbow”, in which a projectile of comparable weight managed to fly 228.6-234.7 meters, and this was with the aid of a significant 9 m/s tailwind which would push the arrow further than it would have gone. These shots managed 131-136 joules. One particular arrow shot from the same 150 lb longbow managed to reach the same range as the 285 lb Han crossbow, but with a significantly lighter projectile of 74.4 grams:




Note that unlike the Han records, the author stated that the longbow shots here were shot at the angle for maximum range.

The reader can also compare this with the reproductions of professional crossbow maker Todd Todeschini. His replica of a 1250 lb Medieval European steel crossbow managed to send an 88 gram bolt 207-215 meters. The crossbow managed around 140 joules. Likewise, the 1200 lb Medieval European composite crossbow replica made by Andreas Bichler, using a cranequin to draw, managed to shoot at 200 joules in freezing weather, but 168 joules in hot weather. The difference in joules, as explained by Mr. Bichler, was due to the weather decreasing the stiffness (and hence draw weight) of the prod. The draw weight of a composite prod increases in cold/dry weather but decreases in hot/humid weather.
 
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HackneyedScribe

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Efficiency and Power
What may surprise many readers is how a reduced 285 lb Han crossbow shoot at the same level of power as a Medieval 1200 lb composite crossbow? And how could a 150 lb longbow shoot at the same level of power as a Medieval 1200 lb steel crossbow? This can be explained by powerstroke. Powerstroke is the length required for a string at rest to be drawn back to the trigger, and Medieval crossbows had short powerstrokes of around 5-6 inches. Short powerstroke means a crossbow quarrel have less time to accelerate before leaving the string. This meant Medieval crossbows must have much heavier draw weights than bows in order to shoot the same projectile at the same velocity. An analogy could be trying to throw a baseball with T-rex arms. Even if the arm could bench press a truck, the speed of the ball would still be limited by the short length of the throwing arm. Strength, like draw weight, isn't everything.
Crossbow-maker Andreas Bichler also confirmed that with crossbow prods of the same draw weight, the one with the lower powerstroke would have more mass (all else being equal), which slows down the prod's shooting speed. Likewise, higher draw weight and a steel structure adds additional mass to the prod (all else being equal), which also impairs how fast the crossbow could launch a projectile. A good analogy to this is a heavy tank trying to outrun a race car. Despite having more horsepower, the weight of the tank (prod) would slow the tank down. Due to this reason, typical crossbows of Medieval Europe generally need many times the draw weight of a bow in order to give a similarly powerful shot. Medieval Europeans addressed this design issue by utilizing winches to maximize the draw weight many times beyond that of a bow.
However, ancient Chinese crossbows used a different trigger design: a triple compound lever turned in on itself. This reduces trigger pull (the force required to press the trigger into releasing the catch), which meant the trigger lever need only be as short as could be comfortably operated, hence allowing the nut of the trigger to be placed near the back of the stock. This resulted in a crossbow design with relatively long powerstrokes rivaling that of a bow, greatly reducing the crossbow’s usual weakness of energy transference inefficiency. Han dynasty crossbows would have a draw length of 24 inches, implying a powerstroke of 18-20 inches. For probably these reasons, crossbow replica maker Todd Todeschini, the maker of the 1250 lb Medieval steel crossbow, did comment that the efficiency of Asian crossbows were “much better”.


Above is medieval trigger, below is Han trigger​

Generally speaking, the power of a bow or crossbow measured in inch lbs = 0.5 x powerstroke length x draw weight. The most commonly mentioned crossbow in excavated accounting records were of the 6 stone (387 lb) type. In comparison most bows would only have draw weights of 40 to 100 lbs. Against armored men, Song dynasty archers could use bows with draw weights of up to 160 lbs, still less than half the draw weight of typical Han crossbows. Furthermore, thanks to the long powerstroke and composite prod, the Han crossbow would have very high efficiencies for a crossbow. Andreas Bichler noted how longer powerstrokes give higher dynamic efficiencies, so even composite prods would have low efficiency insofar that their powerstroke remains short. From this, we have the following result for shooting power

Potential Energy
Heaviest standard 8 stone Han crossbow power = 516 lbs draw weight * ~19 inches powerstroke/2 = 4902 inch lbs
Andreas Bichler's 1200 lb composite crossbow = 1200 lbs draw weight * 7.48 inches/2 = 4488 inch lbs
Tod Todeschini's 1250 lb steel crossbow = 1250 lbs draw weight * 6.5 inches powerstroke/2 = 4062.5 inch lbs
Typical 6 stone strength Han crossbow's power = 387 lbs draw weight * ~19 inches powerstroke/2 = 3676.5 inch pounds
Heavy Song dynasty bow made to pierce armor = 160 lbs draw weight * ~23 inches powerstroke/2 = 1840 inch pounds

The above only shows each weapon's potential energy (energy that is stored at full draw), but does not compare the actual energy released into the projectile. Take note that the potential energy shown is only a linear estimation of the triangular area under the force draw curve, but not the actual area of the force draw curve (which would be non-linear). Why this matters can be gleaned by Andreas Bichler's statement:
A composite crossbow is able to store more cinetic energy like a steelbow - for example my 550kg composite bow is able to store aprproximately 590J. The 500kg steelbow from Ingo Lison (a very excelent german crossbow maker) stores only 390J and his 1000kg steelbow stores 599J.

The below graph explains how using a linear calculation of potential energy (same equation used to calculate the area of a triangle) would miss calculating the total area (Actual Stored Energy):


If we measure actual area, then the potential energy would be higher across the board, with composite prods benefiting much more than steel prods because composite prods have a more prominent "bulge" (pure yellow area) above the linear line. Because we only have the estimated area under the linear line, we stick with calculating linear potential energy. Because this would underestimate how much energy would be imparted into the projectile, dynamic efficiency (the percentage of potential energy that's imparted into the projectile) are adjusted upwards to compensate. So for the information below, just note that actual dynamic efficiency would be lower, but actual potential energy would be higher. The resulting joules are still the same.

Projectile Energy
Heaviest standard 8 stone Han crossbow power = 4902 inch lbs * 55% efficiency = 2696 inch lbs = 305 Joules
Typical 6 stone
strength Han crossbow's power = 3676.5 inch lbs * 60% efficiency = 2205.9 inch lbs = 249 Joules
Andreas Bichler's 1200 lb composite crossbow = 4488 inch lbs * 39.04% efficiency = 1752.3 inch lbs = 198 Joules
Heavy Song dynasty bow made to pierce armor = 1840 inch lbs * 75% efficiency = 1380 inch lbs = 156 Joules
Tod Todeschini's 1250 lb steel crossbow = 4062.5 inch lbs * 30.5% efficiency = 1239 inch lbs = 140 Joules

Dynamic efficiency of Han crossbows is adjusted to 60% partly because that is mid-way between the dynamic efficiencies of composite bows with long powerstroke and composite crossbow prods with short powerstroke.
 
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HackneyedScribe

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Dimensions
The Han trigger mechanism excavated in 1983 in HuanXian had ethcings denoting the trigger to be one for the six stone crossbow. It was made during the Yong Yuan era (89-105 AD). Its length is 12 cm, the width 3.5 cm, the “wangshan” is 7.5 cm, and the handle is 8 cm. It weighs 1,250 grams (2.76 lbs). In comparison, Qin crossbow triggers were only 8 cm in length, but its short length was due to the lack of a trigger box. With a box, its length would approach 12 cm. Qin handles were 8 cm and the wangshan, if counting only from the surface of the stock to the top, is 5.66 cm while the entire thing is 8.24 cm. This means that all else being equal, the trigger pull of Han six stone crossbow triggers were around the same as those found in Qin Shi Huang’s terracotta army.

The Chinese military crossbow’s basic dimensions seem to have stayed mostly the same until the advent of gunpowder firearms. The following is a Medieval passage (CuiWei XianSheng BeiZheng Lu) describing the dimensions of the Divine Arm Crossbow:

Within the stock's teeth it is 1 chi 8 cun (22.7 inches), the gourd head is 4 cun (5.4 inches). The stirrup is 2 chi (25.2 inches). The stock have length 2 chi 3 cun (29 inches), the horn prod have length 4 chi 5 cun (56.7 inches)……

He moves on to speak of crossbows in general:

If the prod is longer than 6 chi and if the stock is longer than 3 chi(38.8 inches), then at the shoulder the crossbow prod will tip toward the ground, and below there is the problem of tripping, when stepping on such a crossbow the stock head will reach the chest, so above there is no pulling strength…… At present day we want to use crossbows with draw strength of 2 stone to 3 stone (~264 lbs to ~397 lbs)…… The crossbow prod should be 5 chi(1.6 meters) to 6 chi(1.9 meters), and cannot be too long, so that short soldiers can easily shoot it at the shoulder.

In comparison, the best preserved ancient Chinese military crossbow was excavated in Qin Shihuang’s terrocotta army in 2015. Its stock length was 70-76 cm (27-30 inches), prod length was 1.3-1.44 meters (~54 inches), prod diameter at the grip was 3-5 cm, prod diameter at the tip was 2-3 cm. Its string length was 1.08-1.24 meters. Judging by its prod shape and length, the crossbow probably had a draw weight in the low couple hundred pounds.

Projectiles

Most bronze weaponry died out during early Han, but throughout the dynasty most crossbow arrowheads were still made of bronze with a metallic tang, inserted into a wooden shaft. Some crossbow bolts were not entirely bronze. Rather, the arrowhead was of bronze while the tang (which sockets the bolt into the shaft) was iron. The reason for this was answered by Donald Wagner, who pointed out the superior casting properties of bronze. Han bronze arrowheads were remarkable for its attention to detail. Their intricate wings placed along the bolt tip were so small yet finely cast that it would be beyond the casting ability of iron for more than a thousand years afterwards.


The two projectiles on the right are Han dynasty crossbow bolts, picture taken by Kenneth from CHF​

Such precise casting techniques allowed a more aerodynamic bolt. Because this aerodynamic design was only required for the bolt tip, having an iron tang would not affect its flight. Therefore, with iron being the cheaper metal, it was only natural for Han metallurgists to design crossbow bolts with a bronze head and an iron tang. Another reason could be that bronze was generally harder than iron, and this hardness was desirable in arrowheads for purpose of armor penetration. The three-sided arrowheads from Qin crossbow quarrels was found to have higher tin concentrations in its arrowhead than in its tang, which meant that the arrowhead was harder. Regarding projectile weight, it was standard for Han crossbow projectiles to weigh 2 liang per stone. This meant that a Han quarrel for its most common crossbow of six stone would weigh 93.75 grams.
 

HackneyedScribe

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Drawing the Crossbow
Yet how was one able to draw these powerful crossbows? Weaker Han crossbows were categorized as ‘arm-drawn’, in that the bow was drawn in a standing position with the two feet grounded on the prod while the arms pulled the string up towards the trigger. These probably had draw weights of around 2-4 stone. More powerful Han crossbows were ‘foot-drawn’, in that the string was drawn in a sitting position using both the legs and the arms. This allowed a much heavier draw weight as the muscles from the legs was much more powerful than those in the arms. Distance shooter Harry Drake used a 300 lb foot bow, drawn similarly to that of foot-drawn Han crossbows, in order to participate in his archery competitions.
The heaviest crossbows would be drawn with a winch. These would no longer be handheld but must be used with a prop or stand of some sort. Immobile crossbows fixed inside military forts on on top of walls were called "Revolving Shooters". Each revolving shooter would have a very thick wooden plank in front of it for protection against enemy fire.


Revolving shooter found in the northern border of Chu-yen
Set up a bamboo fence. In all cases extend it to join the parapet. Make it 6 chi high with spaces 4 chi wide where all those armed with crossbows can take their positions. There should be “revolving shooting machines” which are 6 chi high and buried in the ground 1 chi. Two pieces of wood joined together are used to make protective shields (wen) which are 2 chi long. Through the centres of these drill a hole to accommodate a connecting arm straight against the wall. Every 20 bu there should be one of these (i.e. a “revolving shooting machine” plus its protective shields). [Put someone in charge of it and] order skilled archers to assist him. Not one person is allowed to leave his post. - Mozi
"Yellow Crossbows" was the name given for more mobile devices. The strongest Heavy Yellow Crossbow could have draw weights of 90 stone, implying that its size would probably be akin to that of a ballista.


Eastern Han mural depiction of a windlass crossbow at the bottom center, possibly a lower tier "Yellow Crossbow"
Great Yellow Crossbows, unlike revolving shooting machines, can be used as field artillery. Here is a passage of the Great Yellow Crossbow in action, taking place in which general Li Guang's army was surrounding by a Xiongnu force 10 times the size of his army:

Li Guang ordered his men into a circle facing outward. The barbarians attacked furiously and arrows fell like rain. Over half the Han soldiers were killed, and their arrows were nearly gone. Li Guang ordered his soldiers to draw their strings but refrain from firing, while he himself, using his Great Yellow Crossbow, shot at the enemy sub-commanders, killing several of them, nullifying the Xiongnu advantage. - Shiji

Considering the Great Yellow Crossbow described in this battle was used to snipe enemy personnel, we can say that its draw weight was anywhere from 10 stone (645 lbs) to a couple stones higher. However, the heaviest Great Yellow Crossbow I have read mentioned one Great Yellow Crossbow of 40 stone (2580 lbs)! This was likely much greater in size than lower tier Great Yellow Crossbows, and thus could be interpreted as a siege machine. It is likely that another machine, called Interconnected Crossbow Carriage, would be even more powerful. Interconnected Crossbow Carriages (sometimes translated as the "Joined Crossbow Carriage) was first mentioned in the Mozi, written during the Spring/Autumn to Warring States period. They were described as ballistas with multiple prods placed within a four-wheeled wooden framework, shooting either large harpoon-like arrows with strings attached, or multiples of smaller projectiles at once. By the Han Dynasty, more than 500 of these carriages were described in the military inventory accounting record of Donghai Commandery.

Prepare against the high approach (?the lin or “approacher/overlook cart”) with the “joined crossbow” carriage (liannuche). [This is made of] timbers 1 chi square and is of a length corresponding to the wall’s thickness. It has two axles and four wheels, the wheels being inside the frame. The inside itself is divided into upper and lower levels. Both left and right sides have two vertical posts each, and left and right sides have a horizontal beam. The left and right ends of both horizontal beams all have a tenon which projects straight out for 4 cun. The the left and right the crossbows are all bound to the vertical posts. With a “tooth” all the strings are linked together right up to the main string. The crossbow “arm” (?stock) at the front and back is level with the frame [of the carriage] which is 8 chi high. The crossbow pivot extends below the frame 3 chi and 5 cun. The “joined crossbow” (liannu) control mechanism and its housing are made of bronze [requiring] 1 dan and 30 jin. The string is drawn around a windlass. The size of the frame is 3.5 wei. The the left and right there are “teeth” 3 cun square. The wheels [of the cart] are 1 chi 2 cun thick. The “arms” for the “teeth” are 1 chi 4 cun wide, 7 cun thick and 6 chi long. External to the “arms” and level with the frame there is a “claw” (zhua) which is 1 chi 5 cun long and extends transversely on both sides. It is 6 cun wide, 3 cun thick, and of the same length as the frame. And there is an aiming mechanism which is able to rise or fall and can be directed upwards or downwards. The base of the crossbow weighs 120 jin and is made from timbers 1 wei 5 cun in size. The arrows are 10 chi long and have a cord attached to the end like an yishe which can be wound back by a windlass. The arrows extend above the crossbow “arms” by 3 chi. There is no limit to the number of crossbows. Sixty [large arrows] are fired and retrieved whereas small arrows are not retrieved. Ten men control this cart. When an attack is seen , then the enemy can be fired at from the high towers, whilst on the wall a protective screen is used against enemy fire. -Mozi

Unfortunately, no contemporary picture of the Interconnected Crossbow Carriage was found, but considering the high draw weight, the stronger ones must certainly have multiple prods attached. This allows the draw weight of the ballista to multiply as the accumulated draw weight of each prod was combined together. If the ancient Interconnected Siege Ballista was anything like the Triple prod Ballista shown in Song Dynasty Manuals, then one prod would be placed backwards. Why not have all three prods face the same direction is worthy of consideration. The answer to this is powerstroke. Having one prod placed facing the opposite direction allows the powerstroke to be increased significantly, and I have described in the beginning how powerstroke can increase a ballista's shooting power just as much as the ballista's draw weight. One can see how this works with the following picture:

 
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HackneyedScribe

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Advantages and Disadvantages

The primary strength of the crossbow is without doubt its strong armor penetration capability. With a median draw weight of 387 lbs, and a powerstroke rivaling that of a bow, Han crossbows could shoot a projectile further and faster than that of a bow. According to the Han era government official Chao Cuo, one of the biggest advantages of Han armies over the Xiongnu was that the crossbow could penetrate the leather armor and wooden shields that the nomads possessed.
Furthermore, a crossbow has the option to shoot shorter projectiles. For a bow, the length of an arrow-shaft must be greater than the bow's draw length, or else the bow would not be able to shoot the arrow at full draw. A Han crossbow may very well shoot quarrels with a length rivaling that of an arrow, or it could shoot significantly shorter bolts. This is possible because the quarrel would be launched from the groove of the stock, so a crossbow could even shoot quarrels small enough to be called darts should the occasion warrant it. By shooting shorter quarrels, spent projectiles cannot be picked up by enemy archers to be shot back against the crossbowman. Needham speculates that the East Asian arrow-tube guide (called pyun-chun to the Koreans), was developed by nomadic peoples in order to counter precisely this advantage.
Another advantage is that the crossbow is much easier to aim and shoot than a bow. A bowman must take aim while his arms resist the tension of the string at full draw. Even the strongest bowman could only aim within a limited time frame before his bow arm gives in. A crossbowman can take aim indefinitely, as the tension is held by the trigger. When used in a chariot or ship, the stability that the crossbow provides while aiming no doubt also alleviates the rocking motion of the vehicle involved.
A crossbowman can also draw the string before battle starts, to make sure he is able to take the first shot within a moment’s notice. Examples of this can be found such as when Xiangyu tried to kill the first Han emperor by hiding a pre-cocked pistol crossbow within his clothing. When emperor Wen inspected the military camp of general Zhou Yafu, the sentries were described in the Shiji as ‘in armour and bearing their swords and other weapons, their crossbows cocked and full of arrows’. The advantage to having a crossbow loaded indefinitely becomes particularly useful in sieges, as crossbowmen could use this advantage to take very quick pot-shots when enemies peek their heads from pavises, battlements, or any other protection.

The Han crossbow did come with shortcomings. Han crossbow prods were composite, including sinew and horn materials. Compared to metal prods of winched crossbows in Medieval Europe, composite prods needed more maintenance, as its draw weight would temporarily decrease in hot and humid weather. The long powerstroke also required a very long prod. Andreas Bichler noted how his 617 lb composite crossbow performed very badly because its 75 cm prod was too long for its powerstroke. In addition, the Han crossbow design requires a very long prod (albeit not as long as 75 cm, otherwise the string would be pulling the bow limbs apart rather than storing energy, a case known as stacking). Thus each crossbowman requires more horizontal space for shooting, which forces crossbowmen to either use open skirmishing formation, or adopt special formations to compensate (such as the countermarch, which will be described below).
The high draw weight of the crossbow also makes stringing difficult, particularly when the bow was recurved like those of Han crossbow prods. By the Qin dynasty, this problem was probably alleviated by having a bastard string in addition to the main string, so that the prod could be left partially unstrung to make stringing easier for future use. When shooting at a particularly elevated angle, the stock of the crossbow would block the user's line of sight, diminishing the crossbow's advantage in superior range when it comes to precision shooting. By the late Ming dynasty (~1550s AD) soldiers started using smaller crossbows which drastically reduced this disadvantage, but at the cost of reducing powerstroke very significantly. The biggest offset for the crossbow was its reloading speed. Even when pulled by hand as opposed to mechanical means, a crossbowman would still be outpaced by an archer in rate of fire.

Crossbow Formations

The standard deployment for crossbows would be to have the crossbowmen placed at the flanks of the army, screened by cavalry. In this way they could shoot at the flanks of the enemy. The Han also adopted tactics to offset the disadvantages of their weaponry. To nullify the disadvantage of the long reload time and the requirement for space, Han era soldiers came up with a drill similar to the countermarch:

The drill of crossbowmen alternatively advancing [to shoot] and retiring [to load]; this is something the Xiongnu cannot face’ - Chao Cuo of Western Han, Shiji​

The requirement for horizontal space meant that for a given line of 100 meters, a single volley from the front row would consist of only around 70 quarrels, whereas crossbows with shorter prods could squeeze more crossbows into the front row and hence shoot double that many quarrels in a single volley. The countermarch offsets this by allowing the people at the back rows to participate through the practice of shooting in rotation. The number of quarrels per volley would still be the same, but the Han countermarch formation allows for more volleys within a given span of time. Furthermore, the countermarch gives crossbowmen more time to rest in between shots, and offsets their slow fire rate.


By the late Han new tactics were developed that, when viewed from the front, would look very similar to the square formation of the flintlock era.

When the enemy comes to the deer-barricades, the soldiers must hold their position behind them and thrust with spear and halberds. They must not stand as rising would hinder the shooting of the crossbowmen.-Military Commands (Late Han-3kingdoms period)

With this formation, the open-order formation of the crossbowmen would not be susceptible to melee, as the barricades and crouching infantry in front of them acts like a protective wall. The spearmen and halbadiers in front, not being armed with crossbows, could be packed as densely as they wanted to be, and hence be efficient in prolonged melee. This is especially so when they have crossbowmen shooting over their heads and into the ranks of the enemy.
 
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HackneyedScribe

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Aiming

The aiming of the crossbow was refined by both technology and technique. The Han trigger mechanism is a perfect manifestation of this. The trigger itself is designed to operate like a modern trigger in which stored horizontal energy is transferred into a vertical one. This sophisticated design is perhaps the first of its kind that fully allows both hands to stabilize a ranged weapon when discharging a shot. The trigger also comes with graduated sighting blade and grid sight in order to adjust for target distance, which allows the crossbowman to aim with better accuracy. Liu Chong of the Han dynasty, himself very adept as a crossbowman, described how to use it:
of all the things in the whole wide world, there is none so extraordinary as the principle of sighting. There are three minute points and three small points. The three minute points and three small points are upon the warp and the three small points are upon the weft [analogy to silk looms]. They unite upon the catch of the crossbow. ‘-translation from atarn​


Aim by aligning the arrowhead with the proper line in the sighting grid, the correct line being determined by distance of the target
Nearly 1000 years later, Shen Gua of the Song dynasty unearthed a trigger mechanism with a sighting blade. Using Liu Chong’s method for shooting, he managed to score 7-8 hits out of 10. Shen Gua claimed he could have scored even better with a graduated sight.

Bronze Technology

A handheld weapon that could penetrate armor at a distance would be a technology that the Han military would no doubt want to hold a monopoly over. There are plenty of records which show the government attempting to limit such weapons over a certain grade from being brought outside its borders. But the biggest impediment to the empire’s enemies from mass-replicating Han crossbows would be the manner in which the Han crossbow trigger was made. Ancient Chinese bronze-making technology was unique, in that it derived as an offshoot from its advances in ceramic technology. Whereas the rest of the world used the lost-wax process to create bronzework, the ancient Chinese used the piece-mold process. Both bronze making processes entail pouring bronze into a clay mold, which determines the shape of the bronzeware. What’s special about the piece mold process is that the clay mold could be re-used to make cloned copies of the bronzeware, whereas the clay mold of the lost-wax process would require the clay mold to be destroyed in order to extract the finished product.

The Han crossbow trigger is very intricate, and if any part is off by even a little then the entire mechanism could fail to function properly. The piece mold process allows each individual part of the crossbow trigger to be reproduced again and again in a systematic fashion, with each copy being a virtual clone of the other. In this way trigger parts could be made interchangeable as long as they come from the same cast. Whereas with the lost-wax process, the work and care required to make just one more identical copy of a single trigger mechanism would skyrocket.

Measuring Draw Weight

The Chinese were the first to grade the stiffness of their bows by draw weight. This practice is done by seeing how much weight is added to the string until the string is pulled back to the distance of full draw

Translation: For a bare bow-stave with draw weight of one stone (64.5 lbs), adding sinew will increase draw weight to two stone, and adding horn on top of that will increase it to three stone. The draw length is 3 chi (1 chi is about 9 inches). If the present draw weight of 3 stone (193.5 lbs) with draw length of 3 chi (27 inches), then if strung with a relaxed string on both sides of the bow, each additional stone added will cause it to be drawn by one chi. -From Zheng Xuan Zhu



Crossbowmen

Crossbowmen were not necessarily limited to a ranged role in the battlefield. They may also engage in melee. From late Ming author Cheng Zong You:

Ancient warriors went to war, armed with a Spear, a Crossbow, a Quiver, Poison Bottle, and Arrow Shaving Knife. These items are secured to a leather belt, or carried in a shoulder-bag. Hang the Crossbow and other items at the right-waist. Hold the Spear in formation. Use the Crossbow if the enemy is far. Use the Spear if the enemy is close This is the best way.
After consideration, when shooting with the Crossbow, my (author Cheng Zong You) opinion is that one should discard and place the Spear on the ground. When needed, one can pick up the spear and use the Spear again. If the enemy is close and it is crowded, there will be no impediment. Or, for Spears with a pointed rear-end, it can be thrust into the ground for it to stand straight up, while one is shooting the Crossbow. Then, there won't be any inconvenience of having to bend down and pick up the Spear.
However, we wouldn't know if Spears will always have a pointed butt-end and thus this method of erecting the Spear cannot always be used. Moreover, the Spear is long. If the enemies suddenly rush forward and crowd in one can only thrust where the Spearhead is pointed at. Both left and right sides will be difficult for the Spearmen to thrust.
However, when facing the enemy, there is nothing more advantageous than a long Spear. My opinion is that the Long-Saber will be able to tactically cover the left and right sides of a Spearman. So that both short and long weapons can work together and complement each other. This is the best way to deploy the Spear in battle.
The long Saber is 3 zhang 7 cun long, and it is sashed in the belt at the left side of the waist.
When engaging the enemy with the Long-Saber take one end of the crossbow's prod, and insert it diagonally into the belt at the back. Then draw out the long saber to face the enemy. One can turn and cut at all directions with maximum convenience.........

One can see from the above passage that late Ming crossbowmen were expected to fight in melee while still having the crossbow strapped onto his own person. This is made possible by the small size of the late Ming crossbow. Whereas, the Tang crossbowmen in the Tongdian were expected to engage the enemy in melee by dropping their crossbows onto the ground and picking up his polearms. So pre-Ming crossbows seem too big to both carry it on one's own person AND fight with a polearm, but this also meant the crossbow was much more powerful because the increased size allowed a longer powerstroke.
A division consists of an army of 20,000 people. 14,000 of them are used for battle, making up 180 dui; The crossbowmen fire at the bandits (enemy) when the distance is 150 paces(225m), the bowmen fire at the bandits when the distance is 60 paces (90m), if the enemy come within 20 paces, the crossbowmen and the bowmen puts down the bows and crossbows and order others to collect them. The crossbowmen and bowmen each have a sword-staff, and will pick them up and attack with a shout along with the vanguard companies…..

The Donghai Commandery military inventory slips also heavily implies that Han dynasty crossbowmen used a similar tactic, because its two most common weapons by far is the crossbow and the Pi. The Pi is just a spear, except the spearhead is incredibly, incredibly long (so basically a sword with its handle long enough to be a staff, which is more or less how ancient Chinese records describe the Pi). No other weapon quantity comes even close to the quantity listed for crossbows/Pi within the inventory.

So it seems that wheareas Han/Tang crossbowmen used a single melee weapon that is a blend between the spear and the sword, late Ming author Cheng Zong You advocated that crossbowmen use a mix of the spear and the sword.
 
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HackneyedScribe

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Literature

The Book of Later Han listed some of the most popular works read during the Han dynasty. Two of the lost books are named ‘The Strong Crossbow General Wang Wei’s Way of Shooting’ and ‘The Way of Shooting from Afar with the Interconnected Crossbow [a ballista]’. There are other book titles that mention styles of shooting such as ‘General Li’s Way of Shooting, which may include the art of shooting crossbows. It is unfortunate that all but the title of the books are lost.

Continued Development of Crossbows

The Song dynasty further improved on crossbow technology, adopting a stirrup and even double prod winched crossbows that were handheld. It is possible these double prod crossbows were placed on some sort of stand for winching purposes, but was shot in a handheld manner. A Yuan painting showed arm drawn double-prod crossbows used by demons. Nevertheless, however common or uncommon these crossbows were, the development of the stirrup affected nearly all handheld crossbows:

In the His-Ning reign period [+1068/+1077], Li Ting presented (to the imperial court) the plaited frame crossbow [pien chia nu] [his invention], which looked like a bow, but was armed by means of a stirrup placed against the ground. Its bolts could be shot to 300 paces [500 yards], and two thickness of armour scales could be penetrated. It was called Shen Pi Kung [Magic Stock Bow], and was considered the best of weapons. Li Ting had originally been chief of the Tang-hsiang Chiang tribe, but became an officer of a defence corpse after he had made his obedience to the emperor. Afterwards he died in office, and all his sons were famous on the western frontiers for their bravery

With the onset of gunpowder weaponry, the need for hard-hitting crossbows declined. Arrow shooting firearms using uncorned Medieval gunpowder could shoot at over 800 joules, compared to the 249 joules of the typical Han crossbow. This arrow-shooting firearm was further improved when the Chinese learnt from Vietnamese design after the early Ming conquest of Vietnam. They started used a sabot to improve the gun’s accuracy. The niche for armor penetration was taken by projectiles shot by the force of gunpowder. One can see this by first reading the early Medieval Tongdian and Medieval SongShi and then the Reinassance Ming Yinzong Shilu. In these instances, the Medieval sources mention that crossbows start shooting at long distances whereas bows start shooting at close distances. But by the Ming era, it was arrow-shooting firearms which started shooting at long distances, and it clearly replaced the crossbow in this regard.

The early Medieval Tongdian says: 其弩手去贼一百五十步即发箭,弓手去贼六十步即发箭。若贼至二十步内,即射手、弩手俱舍弓弩,令驻队人收。其弓拿手先络膊,将刀棒自随,即与战锋队齐入奋击。
The crossbowmen fire at the bandits (enemy) when the distance is 150 paces(225m), the bowmen fire at the bandits when the distance is 60 paces (90m), if the enemy come within 20 paces, the crossbowmen and the bowmen puts down the bows and crossbows and order others to collect them. The crossbowmen and bowmen each have a sword-staff, and will pick them up and attack with a shout along with the vanguard companies…..

Medieval era Wulin says: 每战,以长枪居前,坐 不得起;次最强弓,次强弩,跪膝以俟;次神臂弓。约贼相搏至百步内,则神臂先发;七十步,强弓并发;次阵如 之…..
In every battle, the long pikes are at the front. They are sitting and not standing up. Then comes the strong bows, then the strong crossbows, all kneeling. Then comes the Divine Arm crossbows. When fighting bandits within 100 paces, the Divine Arm [crossbow] fires. Within 70 paces, the strong bows fire, and the next formation does the same……

Ming Yinzong Shilu, however, clearly shows that firearms replaced the tactical role of long-powerstroke crossbows: “敌在百步之内,神机枪射之,五十步内,弓箭射之,二十步内,牌枪刀迎击”
"when the enemy is within 100 paces, the [arrow shooting] divine engine guns fire, within 50 paces, the bows fire, and within 20 paces, the shields, pike, and swordsmen engages to attack”


'Divine Gun' from the WuBeiZhi​

In order for Chinese military crossbows to remain relevant, they must fullfill a different niche. By the late Ming, crossbows adopted attributes that were shared by European crossbows, namely the short powerstroke and short prod. However, it was also much smaller than Medieval European crossbows despite having around the same powerstroke, thanks to its compact trigger design passed down from ancient times. As a sign of evolutionary convergence, some European crossbows of the same period (now relegated to sports weapons rather than military weapons) also became smaller as they developed multi-roller triggers which lightened trigger pull, allowing for a more compact trigger. The small size of mid-late Ming crossbows meant that it could be tied to the belt while crossbowmen fought with two handed weapons in melee (long spears or two-handed swords). Compare this with Tang crossbowmen who must drop their crossbows onto the ground before engaging the enemy in hand-to-hand combat. The short stocks of late Ming crossbows meant that they could be shot at an angle without impairing the crossbowmen’s line of sight like that of a bigger crossbow. The prod was also usually made of bamboo lathes tied together, which was less prone to weather conditions but decreased efficiency. For example, the WuBeiYaoLue stated:

For today’s JueZhang crossbow, it can be drawn as long as one has strength. The corporals can learn how to shoot it. The court can learn how to make it so that rain and dew will not harm it. With an arrow set to the string, it can kill men within 10 paces if it is not inferior to the bow

The mid-late Ming crossbow also became easier to shoot because the shorter stock length meant that the weight of the prod was closer to the crossbowman’s center of gravity. Overall, crossbows greatly declined in importance within the military, and its design became more focused on being easy to use, maintain, and carry. In short, with the arrival of hard-hitting firearms, crossbow design shifted away from the 'pure power' focus of earlier designs.


The difference in power was not lost on the late Ming. When they dug up their old crossbows they noticed how they were more powerful than contemporary ones, despite being of lighter draw weight.

"recently at a city in Shanxi province there were several hundred old shenbi crossbows in the tower which has been passed down for over one hundred years. It was created by the previous regime. Even though they are all broken, the instruction system survived but there are no arrows. I followed the instructions and successfully created them. It was made from thick and strong bows and it have a draw weight of around 150 jin, 120 jin, and 90 jin, three total...it can shoot a range of around 300 paces."

By at least the mid-Ming period, military crossbows were few and far between, mostly used by non-Han auxiliaries.
When defending against Yi and Hu barbarians, our country traditionally relied on ranged troops for victory. In ancient times the bow and arrow was not enough, so crossbows and quarrels were introduced. By the Han, the officials have strong crossbow generals and captains who shoot by sound. The machines include Divine Arm crossbows, Great Yellow crossbows, Interconnected Crossbows, and Medicine Crossbows. The Xiongnu called the Medicine quarrels as the Han’s divine quarrels. Ever since gunpowder weapons, crossbows became abandoned.

Yet even with the advent of gunpowder weapons, the effect of the crossbow was not totally lost. Notice how the following looks similar to the countermarch and deer-barricade formations described above?:



Sources used:

Records of the Grand Historian, by Simaqian
The Book of Later Han, by Fan Ye
Chu-yen slips
The Military Storehouse of YongShi’s 4th year Equipment Account Book
Handbook of Oriental Studies, by Donald Wagner
Asian Traditional Archery Research Network, by Stephen Selby
Science and Civilization in Ancient China, by Needham
Journal of the Society of Archer-Antiquaries, Volumes 12-22
Fitting Round Pegs into Square Holes by Klaus Leibnitz
Comments of replica crossbow maker Andreas Bichler
Comments of replica crossbow maker Tod Todeschini
 
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HackneyedScribe

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As for the units of measurement, I converted using the following source: "The Nine Chapters on the Mathematical Art: Companion and Commentary" by Kangshen Shen, John N. Crossley, Anthony Wah-Cheung Lun, Hui Liu

pg 8:


pg 11:

The rest is a simple matter of finding how many chi is in a pace (bu 步) and how many jin is in a stone (shih/tan 石).

For example,
pg 9 of the same book:




So 1 stone = 120 jin = 30,000 grams = 66.14 lbs. My measure of 64.5 lbs is actually slightly lighter than that.
 
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HackneyedScribe

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The Donghai Commandery military inventory slips also heavily implies that Han dynasty crossbowmen used a similar tactic, because its two most common weapons by far is the crossbow and the Pi. The Pi is just a spear, except the spearhead is incredibly, incredibly long (so basically a sword with its handle long enough to be a staff, which is more or less how ancient Chinese records describe the Pi). No other weapon quantity comes even close to the quantity listed for crossbows/Pi within the inventory.

So it seems that wheareas Han/Tang crossbowmen used a single melee weapon that is a blend between the spear and the sword, late Ming author Cheng Zong You advocated that crossbowmen use a mix of the spear and the sword.
To be more specific, here is the entirety of the Han DongHai inventory slip:

Bows&Crossbow:
--------Crossbow: 537,707 (imperial owned: 11,181)
--------Bows: 77,521
--------Subtotal: 615,228
Projectiles:
--------Crossbow bolts: 11,458,424 (imperial owned: 34,265)
--------Imperial owned arrows: 1,199,316 (imperial owned: 511)
--------Subtotal: 12,657,740
Armor:
--------Jia Armor: 142,701 (imperial owned: 34,265)
--------Iron thigh clothing: 255, 1 pair of unique ones
--------Kai armor: 63,324
--------Armored thigh clothing: …ten thousand 563
--------Iron lamellar armor: 587,299
--------Leather armor is 14 jin [7.5 lbs]
Helmets:
--------Helmets: 98,226
--------Horse armor: 5,330
Shields:
--------Shields: 102,551
Polearms:
--------Bronze Ge: 632 (imperial owned: 563)
--------Spear: 52,555 (imperial owned: 2377)
--------Imperial owned sheng: 943
--------Pi sword-staff: 451,222 (imperial owned: 1421)
--------Ji halberd: 6,634
--------YoFang: 78,393
--------Duan: 24,167
--------Subtotal: 614,546
Blades:
--------Sword: 99,905 (imperial owned: 4)
--------JingLu Dagger: 24,804
--------Saw…sabre: 30,098
--------Sabre: 156,135
--------Great Sabre: 127 (232)
--------Subtotal: 311,069
Axes:
--------Iron axe: 1132 (136)
Battle Carts:
--------ChengYuZheng chariots, drum chariots,
--------WuGang chariots:18
--------Soldier’s ChengYu chariots: 24
--------Interconnected Crossbow Carriage: 564
--------Charging chariot: 37
--------Drum Chariot: 4
--------Battle Chariot: 1
--------…chariot: 564
--------…chariot: 1
--------WuGang strong crossbow chariot: 10
--------ZuiBi chariot: 1
--------Battle chariot: 502
--------3 wheeled soldier’s chariot: 1 (168)
--------Tracking: 9
--------High…chariot: 11
--------….chariot: 7
--------….chariot…chariot: 2133
--------Su…heavy chariot: 1993
--------Soldier’s…chariot: 677
--------He chariot: 2
--------FeiLow temporary chariot: 2
--------Subtotal: 7174 (imperial owned 42 + 7132)


The metallic parts of Han dynasty Pi:

 
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HackneyedScribe

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Also, Qin crossbow triggers found in Qin Shi Huang's terracotta army seem to be the same size as the Han six stone (387 lbs draw weight) trigger:



It was excavated in 1983 in HuanXian, now located in the HuanXian Museum. The etchings say that the trigger is for a six stone (~387 lbs)crossbow, and that it was made during the YongYuan era (which is 89-105 AD). The length is 12 cm, the width 3.5 cm, the "wangshan" is 7.5 cm, and the lever is 8 cm. It weighs 1,250 grams (2.76 lbs).

In comparison, Qin crossbow triggers were only 8 cm in length, but its short length is due to the lack of a trigger box (and the box wouldn't contribute to trigger pull). With a box, its length would probably approach 12 cm. Qin levers were 8 cm and the wangshan, if counting only from the surface of the stock to the top, is 5.66 cm while the entire thing is 8.24 cm. So when you judge all the moving parts, the amount of force both triggers were designed to handle seems to be more or less the same.

The three types of Qin trigger lever types Ag1, Ag2, and Ag3 and their lengths(A1): http://discovery.ucl.ac.uk/1412513/1/ant0880126.pdf

Yang Hong in Weapons in Ancient China states that Qin crossbow stocks found in Qin ShiHuang's terracotta warrior pits are all around 71.6 cm. Later findings after the book was published seem to match this. Same author also states that the most common Han crossbow recorded in the Chu-Yen accounting slips were of the 6 stone type.
 
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