Meanwhile the united French and Bavarian armies had gained considerable advantage in Germany, and the Duke of Marlborough resolved to lead his British brigades from the ocean to the Danube, to rescue the Emperor of Germany from the menaced danger. To engage in this splendid undertaking, the ROYAL IRISH regiment marched from Breda on the 5th of May, N.S., and proceeded towards the Rhine; being joined at Bedburg by the detachment from Maestricht. Continuing its route, the regiment proceeded to Coblentz, where it passed the Moselle and the Rhine, and afterwards traversed the minor states of Germany towards the seat of war on the Danube; all Europe being surprised at the ability evinced by the British commander in conducting this daring enterprise.

Having united with the forces of the Empire, the British advanced on the 2nd of July to attack a body of French and Bavarians under Count d'Arco, in an entrenched camp on the heights of Schellenberg, on the left bank of the Danube. About six in the evening the leading division, of which a detachment of the ROYAL IRISH regiment formed part, moved forward under a heavy fire, and attacked the enemy's entrenchments with distinguished gallantry. The enemy made a determined resistance, and the assailants were repulsed; but the attack was renewed with heroic courage, and, after a protracted contest, the Germans co-operated in the attack, when the entrenchments were forced, and the French and Bavarians driven from the heights with great slaughter. The British cavalry, charging, completed the discomfiture of the enemy, and sixteen pieces of ordnance, a number of standards and colours, with the enemy's tents, and the equipage and plate of the Count d'Arco, were captured.

The regiment had one serjeant and eleven rank and file killed; Captain Lea, Ensigns Gilman, Walsh, and Pensant, three serjeants, and thirty-two rank and file wounded.[21]

The victory at Schellenberg was followed by the flight of the enemy from Donawerth; and the regiment was engaged in the operations of the army which penetrated Bavaria, and captured Rayn after a short siege. The Elector of Bavaria formed an entrenched camp at Augsburg, to which city the allied army advanced; but found the enemy's camp too strong to be attacked with any prospect of success, and the troops retired a short distance. The siege of Ingoldstadt was commenced by the Germans, and the ROYAL IRISH regiment formed part of the covering army.

Quitting his camp at Augsburg, the Elector of Bavaria joined a strong body of French troops sent to reinforce his army, and the united divisions encamped in the valley of the Danube, near the village of Blenheim.

At three o'clock on the morning of the memorable 13th of August, 1704, the allied army advanced towards the enemy, and about three o'clock in the afternoon the British developed their attack against the French brigades posted in the village of Blenheim; thus commencing an engagement in which the English troops acquired great distinction. The village being found strongly fortified, it was environed by a few corps, and the army passed the little river Nebel to attack the enemy's lines. The ROYAL IRISH regiment directed its attacks against the right wing of the Gallo-Bavarian army, and was engaged with the chosen troops of France, under Marshal Tallard; its heroic conduct reflected the highest lustre on the British arms, and it contributed materially to the complete overthrow and discomfiture of the opposing host. The French were chased from the field with great slaughter, and the loss of their cannon, baggage, and many troops captured, including the brigades posted in the village of Blenheim: Marshal Tallard, and several officers of distinction, were among the prisoners. The left wing of the enemy was also overpowered by the Germans, and the victory was complete and decisive: the powerful armies of France and Bavaria being literally destroyed. Thus, on the banks of the Danube, was achieved by British valour a trophy which will serve as a monument to commemorate the national glory to the end of time. The conduct of the brave soldiers who conquered in the interior of Germany was the admiration of surrounding states, and has been lauded by numerous historians: the Duke of Marlborough was elevated to the dignity of a Prince of the Roman Empire.

The loss of the ROYAL IRISH regiment was Captains Brown, Rolleston, and Vaughan, Ensign Moyle, five serjeants, and fifty-two rank and file killed; Major Kane, Captains Lepenitor and Hussey, Lieutenants Smith, Roberts, Blakeney, and Harvey, Ensign Trips, nine serjeants, and eighty-seven rank and file wounded.[22]

From the Danube, the regiment traversed the country to the banks of the Rhine, crossed that river at Philipsburg on the 7th of September, and formed part of the covering army encamped at Croon-Weissemberg during the siege of Landau, which was undertaken by the Germans. When the siege drew towards a close, the regiment marched to Germersheim, where it embarked in boats on the Rhine, and in twelve days arrived at Nimeguen, where it landed, and, marching to Ruremonde, passed the winter at that place.