Having reposed a few months in quarters, and received a body of recruits from England, the regiment traversed the conquered territory to Lisle, in June, 1709, and afterwards took part in the manœuvres by which Marshal Villars was induced to reduce the strength of his garrisons in his fortified towns, to reinforce a line of entrenchments and forts, in which he expected to be attacked. This object gained, the siege of _Tournay_ was immediately commenced; and the FIFTEENTH foot, commanded by Lieut.-Colonel Andrew Armstrong, formed part of the covering army; but when the town surrendered, the regiment joined the besieging force, and took part in the attacks on the castle. This proved a desperate service. The citadel of Tournay was celebrated for the multiplicity of its under-ground works, and the approaches were carried on by sinking pits, and excavating subterraneous passages to the enemy's casemates and mines. The soldiers employed on these works were sometimes drowned with water, suffocated by smoke, and buried by explosions; and at other times parties of the besieging force and of the garrison met, and fought with sword and pistol in these gloomy labyrinths. In these services the FIFTEENTH regiment had a number of men killed and wounded; it also lost several men from the explosion of a mine, which destroyed a battery. On the 3rd of September, the citadel of Tournay surrendered; and the army traversed the country towards Mons, the capital of the province of Hainault, leaving the FIFTEENTH and several other corps at Tournay, to level the approaches and fill the excavations. Immediately after this work was performed, the regiment traversed the country towards Mons, and joined the army, on the morning of the 11th of September, at the moment the columns of attack were advancing to assault the enemy's fortified position at _Malplaquet_. This proved one of the most sanguinary and hard-contested battles of the war: the confident and fierce attacks of the allies were made against formidable works, defended with resolution, which occasioned a great sacrifice of life; but eventually the position was forced, and the French army retreated with the loss of many colours, standards, cannon, and officers and soldiers made prisoners. The FIFTEENTH were in reserve on this occasion, and its loss was limited to Brevet Major Leslie, killed, and three or four private soldiers killed and wounded. This victory was followed by the siege of _Mons_, and the regiment formed part of the covering army. The garrison surrendered in October. On the 23rd of October, Major-General Howe was succeeded in the colonelcy of the regiment by Algernon Earl of Hertford, afterwards Duke of Somerset, who had served with reputation at several battles and sieges on the continent. [Sidenote: 1710]