Clinton was aware of the vulnerability of his column. As well as 10,000 soldiers, there was a supply column of 1500 wagons as well as the camp followers who always accompanied an army on the march. The wagon train alone was twelve miles long. Clinton's situation was made worse when he abandoned his initial route, entirely overland, in favour of a march to Sandy Hook, from where he expected to sail to New York. While the old route offered him parallel roads which allowed him to reduce the length of his columns, he was worried that his army would be trapped between Washington's army and another American force that he believed might be coming down from New York.
The problem of the new route was that there was only a single road. This forced Clinton to spread his army out in a single column, leaving the baggage especially vulnerable to attack. The British started on their new route on 25 June in very hot summer weather. The next day they reached Monmouth Courthouse, half way to the coast. 25 June also saw Washington appoint Charles Lee to command the American vanguard. This was not a wise appointment. Lee manifestly considered himself to be a far better candidate for commander in chief. He had only recently been released from British captivity, and his conduct at Monmouth was to cause some to question his loyalty. He had also made it clear that he did not approve of any attack on the British - he did not think the American troops could win success against British regulars. He even briefly refused command of the vanguard. His role in the battle was to end his military career.
On 27 June both sides rested as the heat wave continued. Washington now decided to attack. Lee was given orders to wait until the British began to move, wait for most of the army to leave camp, and then attack the British rearguard as it began to move. However, neither Washington or Lee had any real idea of the terrain that the battle was about to be fought over. The road between Washington and Clinton was divided by three large ravines, with the western and middle ravine cut in half by the road. The road crossed West Ravine on a bridge and Middle Ravine on a causeway. East Ravine was to the north of the main road, north of the Monmouth Court House.
It was to the east of this ravine that the first serious fighting began. Clinton set his vanguard under Knyphausen in motion at about five in the morning. This was followed by the baggage train, and finally the rearguard under Cornwallis, with Clinton present, did not begin to move until eight. What happened next was and is confused. Washington had not issued Lee with clear orders. Lee also failed to issue clear orders to his own subordinates, who after the battle reported that they had no idea what Lee was planning.
The fighting started soon after Cornwallis and the British rearguard started to move. The advancing American troops outnumbered the British rearguard 5,000 to 2,000, but had the disadvantage of having no clear plan. The American troops advanced piecemeal towards the British troops as the commander of each regiment felt fit. In contrast Clinton's early actions were based on the idea that he could defeat the American vanguard with the forces at his disposal before Washington with the rest of the American force could arrive. Clinton knew that Washington was on the far side of the West Ravine and was counting on defeating Lee before the rest of the American army could come forward. He called a part of the vanguard back, and once they arrived planned a general attack.
Clinton's account of the rest of the battle credits the Americans with rather more coherence than the facts justify. According to his report to Germain, the Americans 'fell back and took a strong position on the heights above Freehold Courthouse'. In reality the American retreat seems to have been more chaotic. Lee pulled at least part of his right wing back, without telling his commanders what he was doing. Left apparently unsupported the left wing was also forced to pull back. The withdrawal quickly turned into a near rout. Lee later claimed that the retreat had been a well ordered response to British actions, but his subordinates did not share that view. No orders reached his commanders either before or during the retreat.
This may be because Lee had no clear idea of what to do. The French engineer Duportail, recommended a defensive position on a hill between West and Middle Ravine, but on his arrival Lee felt it to be too vulnerable and no orders were issued. Order was restored by Washington, who was riding ahead of the rest of the American army, and was astonished to find Lee and his force in full retreat. After an apparent display of uncharacteristic anger Washington took command of the situation. The retreating troops were formed in a line to the east of West Ravine. Washington then returned to the rest of the army, still coming up, and formed them into a strong line to the west of West Ravine, in a position defended by swamps and woods.
When Clinton and Cornwallis reached the first American line in the early afternoon, their troops were already tired, partly because of the fighting and partly due to the intense heat, but Clinton felt that he needed to attack in order to protect his retreating baggage. The American line to the east of the ravine was quickly overwhelmed, but the main American position was much stronger. For much of the afternoon the British attacked this line in a series of determined but piecemeal attacks. Clinton and Cornwallis on the British side and Washington on the American repeated exposed themselves to personal danger, Cornwallis even leading a cavalry charge. This level of personal risk was typical of battles of the period.
Eventually exhaustion forced Clinton to call off the attack. Washington tried to organised a counterattack, but his troops too were tired, and by about six in the evening the fighting was over. Clinton was happy that his main objective of the day - to cover his retreat - had been achieved, and the next morning the Americans woke to find the British gone. The rest of the march to Sandy Point went without a hitch, and on 1 July the British army reached the safety of what was then an island, from where they were evacuated to New York.
The significance of the battle of Monmouth is as confused at the battle itself. The main victim was Lee, whose conduct led to a court-martial at which he was found guilty of failing to attack despite orders to do so, of conducting a 'shameful' retreat, and of showing disrespect to the commander in chief. He was suspended from command for a year, effectively ending his role in the war. Both Clinton and Washington could take satisfaction from the battle. Clinton had feared that his retreat from Philadelphia could have lead to another Saratoga. Instead he had fought a battle against a larger American force and inflicted more losses than he suffered. Washington also had grounds to be happy. He had personally restored order to a retreating army, always difficult. His army had then stood its' ground against repeated British attacks and had ended the day in position of at least part of the battlefield. However, both sides also had reasons for concern. The British counterattack had been poorly organised, and in private Clinton was less happy with the conduct of his army. A chance to inflict a decisive defeat on the Americans had been missed. For Washington the start of the battle had been a disaster, and Lee's role an embarrassment. Even with his increasingly well trained army of regulars, Washington had failed to inflict a defeat on a smaller British force, retreated heavily laden with baggage, and on a ground of Washington's own choosing. A second major American victory so soon after Saratoga and with the French about to appear in America would probably have ended the direct British effort against the American rebels.