On 18 December 1742 Mordaunt was promoted to the rank of full colonel of the Royal Regiment of Ireland, which was sent in 1744 to protect the Netherlands against French invasion.

He led a brigade of infantry at the Battle of Lauffeld, and was made a Knight Companion of the Order of the Bath at the end of the War of the Austrian Succession.

A secondary objective was to highlight Britain's capacity to strike at the French mainland, and force France to withdraw troops from other conflicts to defend its western coastline.

[1] Mordaunt was placed in overall Army command for the assault, supported by Major-General Henry Seymour Conway and Colonel Edward Cornwallis.

However, they now discovered that shallow water would prevent the ships from approaching closer than a mile and a half from shore, requiring a long and hazardous landing by boats.

An attack was planned on the basis of a report by Colonel James Wolfe, who had gone ashore at Rochefort with a scouting party and concluded that the French garrison as too weak to prevent the landing.

[2] A second council, called on 28 September aboard HMS Ramillies, reversed this decision and decided on a night attack upon the forts at the mouth of the river Charente, with the first embarkation to be led by Mordaunt in person.

Mordaunt's defence centred on the technicality that his instructions for the expedition did not include an absolute requirement to make a landing.

[2] Mordaunt retained his commission, but having earned the King's displeasure after Rochefort, he never again held a senior field command.