The Battle of Fontenoy was fought at Fontenoy in the Austrian Netherlands on May 11, 1745, during the War of Austrian Succession. French forces under Hermann Maurice, Count de Saxe (the Maréchal of Saxe, an illegitimate son of King Frederick Augustus I of Poland) were besieging Tournay. An Anglo-Dutch-Hanoverian army under the Duke of Cumberland advanced to the relief of Tournay, with the British forces attacking French positions uphill. The French lost 5000 (of 56000 present, including those conducting the siege) men, while the British lost 9000 (of 50000), a defeat for Cumberland's forces. His assault, carried out by 15,000 British and Hanoverian troops, repulsed repeated attacks by the finest cavalry regiments in the Franch Army, including the Maison du Roi, until it was defeated by a counterattack carried out by 5000 men of The Irish Brigade (French) and the Normandy and Vaisseaux regiments of French infantry. The attack against the French centre, had it been carried out with more skill, could have been decisive. As Frederick the Great later remarked, "A quarter- wheel to the left or the right would have brought victory".

The most celebrated anecdote of the battle relates to Sir Charles Hay, a captain in the 1st Foot Guards. On reaching the brow of the incline the columns confronted the French line of Foot. Opposite the 1st Foot Guards were the Garde Francaise. This French regiment had given way at the Battle of Dettingen and in their precipitate retreat had tipped up one of the bridges of boats. Many had drowned. Sir Charles Hay is reputed to have doffed his hat and bowed to the French officers saying: “We are the English Guards. We remember you from Dettingen and intend to make you swim the Scheldt as you swam the Main.” The alternative story is that Sir Charles Hay said “Messieurs les Gardes Francais, s’il vous plait tirez le premier.” Hay was wounded in the battle.

Fontenoy gave the British Foot a reputation for stubborn determination. It caused observers to express surprise at the weak performance of troops at the Battle of Prestonpans and Falkirk later the same year.

Whilst Cumberland's attack on the superior positions of the French army showed little tactical skill and his forces had to retreat, the Duke showed great personal courage.

The brigade which he commanded in the attack included the Scottish Highland Black Watch regiment. Although they had joined the British forces on the continent in 1743, this was their first battle; their courageous determination to press the attack greatly impressed the Duke of Cumberland, and they introduced the then novel technique of hurling themselves to the ground when a volley was fired at them, then leaping to their feet and firing back. This "Highland way" of fighting may have been learned in their previous role of policing the highlands.

However, whilst they were away the Jacobite Rising started and in the autumn of 1745 the Black Watch was moved to the South of England to help with defence plans against any possible French invasion while the British were preoccupied further north.

(NB. This battle should not be confused with the two battles of Fontenay, which occurred at a different location, in 841 and 1944.)