Forbes commanded between 6,000 and 8,000 men, mostly British regular infantry and Provincial (American) troops, including a contingent of Virginians led by George Washington. Forbes, very ill, did not keep up with the advance of his army, but entrusted it to his second in command, Lt. Col. Henry Bouquet, a Swiss officer commanding a battalion of the Royal American Regiment. Bouquet sanctioned a reconnaissance of Fort Duquesene by Major James Grant of Ballindalloch, acting commander of the 77th Regiment of Foot (Montgomerie's Highlanders),
The next morning, Grant divided his force into several parts. A company of the 77th, under a Capt. McDonald, approached the fort with drums beating and pipes playing as a decoy. A force of 400 men lay in wait to ambush the enemy when they sallied out to attack McDonald, and several hundred more under the Virginian Maj. Andrew Lewis were concealed near the force's baggage train in hopes of surprising an enemy attack there.
The French and Indian force was, in fact, much larger than anticipated and moved swiftly. They overwhelmed McDonald's decoy force and overran the party that had been meant to ambush them. Lewis's force left its ambush positions and went to the aid of the rest of the force, but the French and Indians by then had gained a point of high ground above them and forced them to retire. Grant and Lewis fell back to their baggage train and tried to make a stand there, but their force was too demoralized, and most fled. Grant and Lewis were captured, nearly 300 other British and Provincial troops were killed or captured, but over 500 returned to rejoin the main army under Forbes and Bouquet.
Though the French had beaten off the initial British attack, de Lignery understood that his force of about 600 could not hold Fort Duquesne against the main British force of more than ten times that number. The French continued to occupy Fort Duquesne until November 26, when the garrison set fore to the fort and left under the cover of darkness. As the British marched up to the smoldering remains, they were confronted with an appalling sight. The Indians had cut off the heads of many of the dead Highlanders and impaled them on the sharp stakes on top of the fort walls, with their kilts displayed below. The British and Americans rebuilt Fort Duquesne, naming it Fort Pitt after the British prime minister William Pitt who had ordered the capture of that strategic location.