A strong detachment of recruits replaced the losses of the regiment, and it was in a highly efficient state when it took the field to serve the campaign of 1709. The Duke of Marlborough menaced the French army with an attack, which occasioned Marshal Villars to weaken the garrisons of the fortified towns to strengthen the army in the field, when the allies besieged _Tournay_. The EIGHTEENTH were detached, under the Prince of Orange, to drive the French detachment from Mortagne and St. Amand, and, having accomplished this service, joined the besieging army, and carried on its approaches at the seven fountains. The regiment was engaged in storming the breaches in the Ravelin and Half-Moon; and on the 29th of July it was in readiness to take part in storming the town, which was prevented by the surrender of the place, the garrison retiring into the citadel. The EIGHTEENTH took part in the siege of the citadel of Tournay, which was celebrated for the extent of its underground works. Captain Parker, of the regiment, states in his journal,--"Our approaches against this citadel were carried on mostly underground, by sinking pits several fathom deep, and working from thence until we came to their casemates and mines. These extended a great way from the body of the citadel, and in them our men and the enemy frequently met, and fought with sword and pistol. We could not prevent them springing several mines which blew up some of our batteries, guns and all, and a great many men, in particular a captain, lieutenant, and forty (the London Gazette says thirty) men of our regiment." The EIGHTEENTH lost a lieutenant and several men in the combats underground; and ten grenadiers were suffocated in one of the galleries. In the early part of September the governor surrendered.