Persuaded that the bulk of the Anglo-American army would use the old Braddock route, the French commander in the Ohio, François-Marie Le Marchand de Lignery, was initially troubled by Forbes' deliberate pace. But when he discovered that Forbes had built a new route Lignery immediately adopted harassment tactics to further slow his progress. Soon Anglo-American soldiers who strayed from their camps fell at the hands of the allied Amerindians, who were constantly on the lookout at the edge of the forest. To boost the morale of the soldiers, who were losing their courage in the face of the terror, a raid was organized on Fort Duquesne. On September 14 Major James Grant, with a party from his 77th Highlanders Regiment and a group of American militiamen, some 800 men in all, reached the environs of the fort and decided to wait for nightfall to attack. But Lignery and his second in command, Captain Aubry, were not fooled. Grant and his men were quickly surrounded by approximately 500 soldiers from the Compagnies franches de la Marine, Canadian militiamen and Amerindians "letting out cries like Savages." The battle was described as "heated and tenacious." 
The Scots were virtually wiped out, with 300 men dead in the field and 100 prisoners, including Major Grant himself, not to mention the numbers who took flight. The French had only 16 dead and wounded.
On October 12, on the strength of this victory, Captain Aubry, leading 450 soldiers and militiamen and 100 Amerindians, organized a raid on Fort Ligonier. The British and Americans, who had to take refuge in the fort, were powerless to stop them, and for two days watched their camp being destroyed and pillaged. One month later, another raid by some 30 Canadian militiamen and approximately 140 Amerindians caused so much confusion that the Anglo-American regiments fought one another, each side believing the other to be the enemy!