Having landed at Carrickfergus on 14 June 1690, King William marched south to engage the Jacobite army along the River Boyne on 1st July 1690.The Field.
As William advanced the Irish retreated before him so that by 30 June his army reached the top of a hill near the southern frontier of County Louth. In the valley beyond was the River Boyne marking the boundary of Louth and Meath. Down the Boyne at Oldbridge the river could be forded. William viewed the terrain and thought it suitable for a battle which should be short and conclusive.
The two kings had advantages over one another. James had the stronger position, but his troops appeared to be inferior in quality and quantity. He had about 30,000 men of which a third were very good French infantry and equally fine Irish cavalry.
William had 36,000 men of various nationalities and languages.
When William studied the enemy across the Boyne he agreed with his generals that they were not impressive to look at, but added, "They may be stronger than they look, but weak or strong, I will soon know all about them." The Irish recognised William and a marksman fired at him. When it struck the gun holster of Prince George of Hesse William cried, "The poor prince is killed." As he spoke a second shot tore his coat, grazed his shoulder and drew blood. When William slumped over the Irish thought that he had been killed. His men were shocked but quickly relieved when he said "There is no harm done, but the bullet came quite close enough." His injury did not prevent him spending nineteen hours in the saddle that day.
Having assured himself that his men were as ready for battle as he was he advised his officers that he intended to engage the enemy.
The armies began to move at 4 a.m. on 1 July. William ordered his right wing, under the command of Meinhart Schomberg, a son of the old duke, to march to the bridge at Slane, a few miles up the river. The troops were to cross there, and to turn the left flank of the Irish army. James anticipated the move and dispatched Sir Neill O'Neill, nephew of Tyrconnell, with a regiment of dragoons to turn the Williamites back. But when O'Neill received a mortal wound his men fled to make clear the way for the forces of King William.
Lauzen, the French commander, feared that William's right wing would come up at the rear of James' forces, and decided to march with his French soldiers and Sarsfield's cavalry in the direction of Slane Bridge. This decision meant that the fords near Oldbridge were left to be defended only by the Irish foot soldiers. When the battle was joined they were easily defeated. Richard Hamilton put himself at the head of the cavalry and under his command they tried to change the course of the battle. Fighting desperately in the bed of the Boyne against Solmes' Blues they drove the Danish brigade back and successfully attacked the Hugenots.
Duke Schomberg, watching from the Northern bank, decided that the situation needed a general's intervention and though not wearing defensive armour he rode into the fray crying, "Come on, gentlemen, there are your persecutors." These were his last words, for after being circled by Irish cavalrymen, when they moved on he was found dead, killed by two sabre wounds on his head and a bullet in his neck.
King William arrived, where the battle was hottest, in his presence the tide was turned in his favour.
Lord Macaulay said of William, "One of the peculiarities of this man, ordinarily so saturnine and reserved, was that danger acted on him like wine, opened his heart, loosened his tongue, and took away all appearance of restraint from his manner. On this memorable day he was seen wherever the peril was greatest."
On the other hand James, with his reputation as a soldier, was so concerned for his own safety that he stayed well away from the heat of battle.
When he realised that he was defeated at the Boyne he deserted the scene of battle and made for Dublin with a bodyguard commanded by Sarsfield. He was followed by his troops who had suffered fewer losses than might have been expected. A reason for that was that William did not pursue them with the kind of enthusiasm and energy he had shown in war.
The losses of life at the Battle of the Boyne were much less than that of any battle of equal importance.
The Battle of the Boyne was the most famous of Irish battles, for it represented in the Europe of the day a signal success for the Grand Alliance against Louis XIV.
The drama of two kings fighting at an Irish river for an English throne was a sensation in itself. The fact that they represented the two major power groups in Europe, and were supported by international armies, gave the Boyne universal significance.
The flight of James and William's triumphal entry into Dublin had all the marks of an overwhelming victory.
With William's victory at the Boyne the fate of James was sealed.