Before the smart bomb, before the Exocet missile, before the machine gun, before the musket, the English led the rest of the world in one devastating weapon of war: the longbow. In Europe, the bow reached its zenith as a weapon in the 15th century. Traces of archery’s historical importance linger in English surnames such as Archer, Arrowsmith, Bowman, Bowyer and Fletcher, and in the many villages that have areas with names like Butt Lane or Butt Green (where archery was practised).
It is also thought that the V-sign originated with the archers of the Hundred Years’ War against France from 1337 to 1453. The English archers used these two fingers to draw their bowstrings; the French threatened to cut off those of anyone they caught. The robust response was to wave the fingers at the enemy, as if saying: ‘Here they are – come and get them.’
By 1300, the crossbow had largely displaced the longbow on European battlefields, despite being banned in 1139 by the Pope as ‘deathly and hateful to God and unfit to be used by Christians’. The crossbow, though much smaller than the longbow, is a more powerful weapon. The bowstring is drawn back mechanically on a ratchet and so requires less skill and strength to operate. But the drawback is the time it takes to draw and shoot – about a minute, compared with as little as six seconds for a longbow. In medieval England the virtues of the longbow were better appreciated, and by the time of Henry V (who ruled from 1413 to 1422) it had reached an advanced state of development.
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The longbow’s most famous moment was probably at the battle of Agincourt. By October 1415, King Henry’s French campaign had run into trouble and he was attempting to lead his small army northeast along the coast to safety at Calais. The ford across the Somme at Blanchetaque (near Abbeville) was too heavily defended, and he was forced to march almost 100 kilometres upstream before he could cross the river. From here, the army made directly for Calais, but meanwhile a force of around 50 000 under Marshal Boucicault and the Constable of France was advancing on the English. Henry’s army, having marched over 400 kilometres in 17 days on inadequate provisions, was in poor condition: most of his men had dysentery, and Henry, having no wish to fight, offered to buy peace. The offer was refused, and so the two armies met at Agincourt.
The battle which took place early in the afternoon of 25 October was a remarkable one. Henry’s army of no more than 6000 men defeated a better-rested army five to ten times larger, killing about 15 000 French soldiers while losing only about 300 men. The French made virtually no use of archers, whereas the English army was almost entirely composed of longbowmen. Military historians still debate the precise reasons for this astonishing outcome, but it seems clear that the French tactic of opposing the English longbows with heavily armoured cavalry and infantry was a fatal error.
The medieval longbow was a round wooden stave, typically between 168 and 183 centimetres long, tapered towards the ends, which were tipped with horn. It was bowed into a gentle arc by the bowstring, which was made of linen and had loops at its ends which were passed round grooves in the horn tips. The string was 3 to 4 centimetres shorter than the distance between these grooves measured along the bow, causing the bow to bend about 15 centimetres away from the string. The arrow had a wooden shaft, typically 71 to 76 centimetres long, with an iron head and a slot called the nock at the back into which the string was fitted. Near the nock were three vanes, usually made of goose feathers, to stabilise its flight.
SWIFT AS AN ARROW
The archer would fit the nock over the bowstring, draw it back fully, aim, and release the bowstring, thus transferring most of the elastic energy stored in the deformed bowstave – possibly also some of the energy stored in the string – to the kinetic energy of the arrow. A longbow is slightly less efficient than an ideal spring. The potential energy stored within it depends on the force required to pull back the bowstring – called the draw weight by archers, and not to be confused with the bow’s physical weight – which in turn varies with the distance the string is pulled back. If the maximum draw weight is F when the string has been drawn a distance d, the ideal spring stores energy E = 0.50 Fd; a longbow typically stores 0.40 Fd to 0.45 Fd.
What release speed does this imply for the arrow? Accurate calculations are difficult because at the instant the arrow leaves the bowstring parts of the bow itself are moving. But a formula that accounts for this effect indicates that almost half of the potential energy in the bow is ‘wasted’. The arrow-velocity formula has important implications for the material from which longbows were constructed. It shows that to impart a large velocity to the arrow, the ratio of the potential energy of the bow to its mass should be large. This ratio is the elastic energy stored per unit mass of the bow, and for a given material the maximum value of this quantity is determined by its elastic modulus, density and tensile strength. The ideal bow should thus be made of a light, springy, strong material. In medieval Europe the wood of the yew tree was recognised early on as having the best performance in this respect.
But how powerful were the bows used to such devastating effect at Agincourt? Until quite recently, all the evidence was indirect, since no bowstaves from the period had been found. However, a number of contemporary arrows were available, and measurements of these allowed some deductions to be made about the draw weights of the bows for which they were intended. This is because an arrow must be ‘tuned’ to its bow.
The diagram shows in an exaggerated way how this arises. At the top is a view of a bow and arrow from above, just before the archer releases the bowstring. The force exerted on the arrow by the string acts directly towards the centre of the bowstave, so a completely rigid arrow would move as shown in the middle diagram and hit the bowstave. But this does not happen because of the ‘archer’s paradox’. The arrow is not completely rigid, and the force exerted by the string does not pass through its centre of mass, so as soon as the archer releases the bowstring, the arrow begins to bend in flexural oscillations along its length – as shown in the bottom diagram.
The frequency of these oscillations (typically between 50 and 100 hertz) depends principally on the stiffness of the arrow. A correctly ‘tuned’ arrow will bend away from the bowstave as it passes. Clearly, the oscillation period must be matched to the time taken for the arrow to be accelerated past the bowstave, so there is a link between the draw weight of the bow and the properties of the arrow. Calculations suggested that the heavy, 60-gram war arrows of the type used at Agincourt could have been shot from bows with draw weights of over 45 kilograms, but this seemed an unreasonably large value; until about 1980 a figure closer to 35 kilograms was thought more likely.
HIGH VELOCITY BOWS
However, that changed following the recovery in 1982 of the Mary Rose, Henry VIII’s flagship which sank in the Solent in 1545. Over 100 longbows and 3000 arrows were recovered from the wreck, and numerical modelling by Bote Kooi of Groningen University has confirmed that the bows would have had draw weights ranging from 45 kilograms to a truly astonishing 80 kilograms. And there seems no reason to believe that the bows used in Henry VIII’s day, when English archery was already in decline, would have been significantly more powerful than 130 years earlier when archery was at its peak.
The heavy arrows shot from these powerful bows would have had initial velocities ranging between 45 and 55 metres per second (160 to 200 kilometres per hour). With no air resistance, their maximum range would be 200 to 300 metres. However, air resistance is significant. In the early 1980s Alvin Wilby and I made wind-tunnel measurements, at the Cavendish Laboratory in Cambridge, of the aerodynamic drag on replicas of Agincourt arrows which showed that the drag is proportional to the square of the speed, and calculated an actual maximum range of between 150 and 200 metres – the sort of range claimed by medieval archers. Further work showed that the arrows would have arrived at their target at a speed of about 35 metres per second (130 kilometres per hour) and at an angle of about 50 degrees to the horizontal.
What damage would be done by 60-gram war arrows arriving at these velocities? The arrowheads used at Agincourt were of the type known as the ‘long bodkin’ – essentially a square iron spike up to 10 centimetres long, with a mass of about 20 grams. Studies by Peter Pratt, professor of crystal physics at Imperial College have shown that medieval arrowheads were actually made of a surprisingly high quality steel, presumably produced by the combination of heat treatment and forging the head on a wooden block. This would have made them both hard and tough, properties necessary to penetrate armour without breaking. Measurements by Jones and others suggest that provided the blow was not too glancing, long bodkin arrows travelling at 30 metres per second would penetrate armour up to about 1.5 millimetres thick.
Nevertheless, many arrow wounds would probably be at least temporarily disabling, and perhaps one in fifty or a hundred would be fatal. Against unarmoured men or horses the effect would be devastating. With 5000 English archers capable of shooting about 10 arrows a minute, the French would have faced a storm of around 800 arrows each second. It does not take much imagination to visualise their terrifying effect.
