Throughout the period he had been unable to out-manoeuvre the much larger and growing French Army, whose commanders the Marshal Boucicault and Constable d’Albret had long maintained their tactical advantage North of the Somme.

The English Army numbering about 6000 men had behind them a gruelling march during most of which it had rained. They were hungry, exhausted and many suffered from dysentery.

The much larger French Army of some 20 to 30000 men blocked its progress to Calais. It was encamped in a position that left King Henry little choice.

He could neither retreat into the heavily fortified town of Hesdin, nor could he turn either East or West.

The French commanders had not closed their army right up to the woods on either side, but were to the North of its narrowest point. They had thereby left themselves some room for their cavalry to carry out a flanking sweep in order to roll up the wings of the English army where the archers were likely to be concentrated.

The danger posed by English longbow men was well known and had been written up in some detail in what has become known as the Somme battle plan. There seems little doubt that Boucicault in particular was aware and had favoured simply starving the English rather than to engage them in a pitched battle. The French commanders may not have been fully aware that of the 6000 English, over 5000 were longbow men.

However, on that very evening of 24 October the French commanders had made their first error. The site they had chosen was narrow and their position to the North had left the English the option to close their army up to the woods at the narrowest point of the site. Were the English to do so then a flanking sweep by the French cavalry would become much harder to execute.

Moreover, the chosen ground was heavy sticky clay, which was going to make it hard going for the cavalry.

The latter problem was greatly compounded by the exercise of horses during the night preceding the battle, thereby further churning up the soil in front of the French lines.

After a stand-off of some three hours on the morning of the battle, King Henry ordered his army to lift its stakes positioned in the ground and advance some 870 yards/800 metres.

That brought it to within approximately 330 yards/300 metres from the French position. Crucially this advance brought the flanks of the English Army right up to the woods on either side and did so at the narrowest point of the battlefield. King Henry had thereby used the opportunity the French commanders had given him.

The cavalry was in essence the nobility, who brushed aside the command structure. The second major error was now in the making.

The cavalry was massed in anger, in a hurry and its charge was therefore undermanned. Of the 2000 to 2500 available cavalry only 400 to 500 made the charge.

As the cavalry gathered pace the longbow men held their arrows. The order to shoot was given when the horses were within bowshot at 220 to 240 yards (200 to 220 metres). From then on volleys of arrows were loosed.

The wounded horses panicked, riders were thrown, killed or suffered agonizing wounds. The cavalry was thrown back and trampled into the tightly packed advancing footmen.

The heavy churned-up ground slowed the advance of the footmen, critically lengthening the time they were exposed to the arrow volleys before they could lock into combat.

The third error now became apparent. 
The footmen were unsupported by the many longbow and crossbow men in the French army, which had been placed behind the front line. With the kinetic energy of the cavalry broken and the possibility of an offensive by arrow neutralised, too much depended on the footmen.

The narrowness of the battlefield pushed together the overlarge French Army as it advanced into the narrowest part of the battlefield between the woods of Tramecourt and Agincourt. That further aggravated the lack of arm-room the footmen had to wield the weapons of hand to hand combat effectively. The equipment was heavy and their field of view limited by narrow visors. The sticky churned-up ground sapped their energy.

A final error now unfolded with disastrous consequences. Men at the front were squeezed up to the English by their own lines pressing from behind them, trampling men underfoot and further inhibiting the ability of those still standing to wield their weapons effectively. Nevertheless, the English were pushed back some distance by the sheer weight of the French army.