The longbow outflanked
The sound of gunfire assisted French commanders to effect a successful concentration on two fronts, one of which could not offer the longbows sufficient protection. Kyriell as commander of the English army landed at Cherbourg in 1450 with a mere 2500 men.
He had to persuade the Duke of Somerset as Governor of Normandy to augment these numbers by a further 1800 men, which the latter reluctantly agreed to.
Kyriell’s total force was therefore just over 4000 strong of which some 2900 were longbow men.
To the South of the Cherbourg peninsula there were two French armies preparing to engage the English. The Count of Clermont was at Carentan, 20 miles west of Bayeux and 30 miles south of Cherbourg with a force of some 3000 men.
A second force of 2000, under the Constable of Richemont had departed from Coutances, 20 miles further south of Carentan to join de Clermont's army. De Richemont was the older and more experienced commander and had participated in the sudden defeat of the English in the battle of Patay.
The direction of Kyriell's march headed for Bayeux and brought him near Carentan by the 12 April. The Count of Clermont refused to engage the English in spite of being urged to do so by the town’s people. In the end it had been left to the town’s militia to make a sortie at the rearguard of Kyriell’s army, which was repulsed as he by-passed the town. On 14 April heading Eastwards, Kyriell's army camped near the village of Formigny about 10 miles from Bayeux. De Clermont remained at Carentan 15 miles West. Meanwhile de Richemont was moving through St. Lô 19 miles Southwest, in an effort to join Clermont and intercept the English before they reached Bayeux.
Having crossed the estuary of the river Vire, Kyriell and his army camped for the night in a shallow valley in which the small village of Formigny is situated. He was only 10 miles from Bayeux. The lie of the land meant that it was not a good place to oppose an enemy. Indeed one might wonder why an experienced soldier like Kyriell did not continue his march to the safety of Bayeux. It was half a day’s march away. It may have been the case that Kyriell was not aware of the nearness of de Richemont’s army only 19 miles to the Southwest and wanted the opportunity to engage and destroy de Clermont’s battle. De Clermont had however managed to get word to de Richemont of the movements of the English and requested that the latter come to his support in an attack the following day.
De Cleremont advanced East and approached the English camp in the afternoon of 15 April at approximately 3 o’clock. Alerted by his outposts, Kyriell drew up his army in the long-tested formation used since Crécy. About 800 men-at-arms were placed in a dismounted position among three wedges of longbowmen. Allowing for the presence of some billmen, the English had close to 2900 archers who took positions behind planted stakes and shallow moats. With a front estimated at some 1000 (914m)s, the English stood in a dip and had their backs to a brook that ran South to the Aure river. A stone bridge over the brook appears to have been about the mid-point of the English line. As at Patay, the English were in low-lying land without natural features to protect their flanks. There was no reserve, the number of men at arms on foot was too small for that to be possible.
De Cleremont first made a dismounted attack, which was fairly quickly repulsed. The longbow men exacted a heavy toll with enfilading shot from the line of ditches and potholes at short range, as well as from both flanks on each side of the road.
The second charge by de Clermont was mounted and aimed for the flanks of the English. It met the same fate and was driven back. After an interval at about 5 o’clock de Clermont brought up two 'culverin' guns. Most probably these were light guns on two-wheeled carriages. It is also likely they were breech loaded, as they were apparently able to deliver a sufficiently rapid rate of fire to disrupt the English longbow men. Crucially these ‘culverins’ were able to do so beyond effective bowshot range at some 400 yards (366m).
The longbow men were unable to deliver any return shot. After being galled and suffering casualties, the English archers broke ranks and charged the French positions. It is said that they succeeded in seizing both guns. Accounts differ on whether the French recaptured the guns in a counter attack. However, the French Army had by this time suffered losses and had begun to withdraw.
It is likely that if at this point Kyriell had made a brisk counter-attack then the French lines would have been shattered. It is not known whether this omission was due to hesitation on Kyriell’s part, or to his belated awareness of de Richemont’s approach from the South.
It was by now between 6 and 7 o’clock in the evening when both the English and French became aware of Richemont's approach just beyond the horizon to the South. It is likely that de Richemont had located the precise position of de Clermont by the sound of his army’s gunfire. De Richemont was an experienced commander and he immediately rode forward to make contact with de Clermont prior to committing his army. After a quick war council de Clermont agreed to place himself under the orders of the older and more experienced Constable de Richemont, who persuaded de Cleremont to rally his army.
Without reserves Kyriell had no option but to form a new flank. He had in effect to extend his men in a semi-circle, so as to hold against Clermont's army to the West and engage the oncoming attack of the newly arriving French force from the South. It had to be done quickly. The extended semi-circular front of the English was as detrimental to delivering concentrated archery shot, as it was by now unavoidable.
It was a hastily assumed position and could not be adequately consolidated with potholes and stakes. Moreover, Kyriell’s force was by now out-numbered. De Richemont's battle consisted of heavy cavalry and reached the field with an estimated strength of about 1200. Another 800 archers had not been able to keep pace with his mounted contingent.
De Richemont’s battle was deployed on top of a slight ridge by a windmill to the South of the village. He advanced downhill towards the English left while in the process extending his left flank in order to make contact with de Clermont’s right flank. The unfolding attack was in full view of de Clermont’s battle and doubtlessly stiffened morale. The two-pronged attack overcame the now much thinner a line of English defenders. Kyriell’s men fell back everywhere towards a little stone bridge and nearby orchards where heavy fighting took place. The English were cut up into small groups many of which fought to the death. Kyriell was taken prisoner; his entire army was captured, killed, or fled along with the second in command, Matthew Gough to Bayeux.
The defeat was a classic example of two armies affecting a concentration on the battlefield. Although classic in theory it was a manoeuvre that commanders even Centuries later warned against. The reason is that exterior concentration needs good communications. The battle of Formigny is all the more remarkable for the fact that it occurred in virtual absence of communications as was inevitable in the Middle-Ages.
Although the presence of guns significantly influenced the course of the battle they were decisive only in that their noise located the English position precisely and therefore made a concentrated attack on two fronts possible. The issue was then decided by time-honoured hand to hand combat.
Losses on the French side were surprisingly low and are estimated at approximately 200. The number does not seem to fit the initial description of the first phases of the battle, when de Clermont’s army was said to have been repulsed with heavy losses.
On the English side casualties were catastrophic. Some 2500 men were killed and 900 captured. Few were left to flee towards Bayeux. News of the virtual annihilation of Kyriell's army spread rapidly to London.
It left the English without a force in France to protect their holdings in Normandy. Bayeux did not hold out for long, neither did the small number of remaining strongholds. Within a few months after the battle of Formigny the entire region fell to France.