Hundred Thousand Sons of Saint Louis

The organisation of the expedition's command structure posed many problems. Pro-Bourbon commanders had to be given the full chance to exercise the roles they had so recently been given by the Bourbon Restoration without compromising the army's loyalty or efficiency. The solution was to give the secondary commands to royalist former émigrés and Vendéens, and the primary ones to former generals of the Revolution and First Empire. Despite his lack of military experience, the Duke of Angoulême, whose father was heir to the throne, was made commander-in-chief of the Army of the Pyrénées, but he agreed to a role overseeing only the political direction of the expedition, leaving its military direction to Major-General Armand Charles Guilleminot, a tried-and-tested general of the First Empire.

Four of the five army corps were placed under generals who had fought for Napoleon – Marshal Nicolas Charles Oudinot, Duke of Reggio; General Gabriel Jean Joseph Molitor; Marshal Bon Adrien Jeannot de Moncey, Duke of Conegliano; and General Étienne Tardif de Pommeroux de Bordesoulle. The Prince of Hohenlohe commanded the Third Corps, the least-trusted of the five, with only two divisions and 16,000 men (as opposed to three or four divisions and 20 to 27 thousand men in the other corps).

The expedition was made up of regiments in which many of the officers, NCOs and men had been marked by memories of the Napoleonic Wars and so were disposed more kindly towards the liberals than were the French and Spanish Bourbons. The liberals hoped to dissuade the Frenchmen from fighting "for monks, against liberty". Villèle was worried at their propaganda in bars and billets, as a song by Béranger spread throughout March and April inciting the French soldiers to mutiny:

The Duke of Angoulême during the French intervention in Spain

Taking of Pamplona, 1823 (by H. Vernet)

On 6 April, the doubts of some and the illusions of others dispersed. On the banks of the Bidassoa, 500 liberal French and Piedmontese men faced off against the forward positions of the 9th Light Infantry Regiment. Brandishing a French Tricolour flag and singing La Marseillaise, they incited the soldiers not to cross the frontier. The King's infantrymen hesitated until General Louis Vallin rushed to them and ordered them to open fire. Several of the demonstrators were killed and the others dispersed. Many of them joined Englishmen under Colonel Robert Wilson, Belgians under Janssens and other French or Italian volunteers to form a liberal legion and a squadron of "liberty lancers" to fight beside the Spanish constitutional forces. The following day, on 7 April, the "100,000 Sons of Saint Louis" under the Duke of Angoulême entered Spain without opposition from the constitutional government's forces and with the support of the middle classes and part of the urban population.

In the north, Hohenlohe's 3rd Corps (reinforced in July by Lauriston's 5th Corps) forced General Morillo to retreat before rallying his troops. The French were left in control of the rural parts of Navarre, Asturias and Galicia; however, lacking siege equipment, they were unable to blockade the towns, where the liberals continued to resist for several more months. The city of A Coruña surrendered on 21 August, Pamplona on 16 September, and San Sebastián on 27 September. To the east and the southeast, General Molitor pushed back General Francisco Ballesteros into Aragon, pursuing him as far as Murcia and Granada, winning an engagement at Campillo de Arenas on 28 July and forcing his surrender on 4 August. At Jaén, he defeated the final columns of Rafael Riego, who was captured by the Absolutists on 15 September and hanged in Madrid on 7 November, two days before the fall of Alicante. In Catalonia, Moncey managed to quell General Mina's regular and guerrilla forces, with Barcelona surrendering only on 2 November.

More decisive operations spread across Andalusia, since it was the site of Cádiz, transformed into the Constitutionalists' provisional capital and thus the French force's main strategic objective. It contained the Cortes and the imprisoned king and was defended by a garrison of 14,000 men. At first Riego, then Generals Henry Joseph O'Donnell, Count of La Bisbal, Quiroga and Miguel de Álava led the action. Access to the city was protected by the batteries of Fort Santa Catalina and Fort San Sebastian to the west, Fort Santi-Pietri to the east and above all by the fortified peninsula of Fort de Trocadéro, where Colonel Garcés positioned 1700 men and 50 guns.

Under the command of General Étienne Tardif de Pommeroux de Bordesoulle, soon joined by the Duke of Angoulême and Guilleminot, the infantry of generals Bourmont, Obert and Goujeon, the cavalry of Foissac-Latour, the artillery of Louis Tirlet and the engineers under Guillaume Dode de la Brunerie took up positions before Cádiz from mid-July. Forced to use several naval divisions for surveillance of Spain's Atlantic and Mediterranean ports and coasts (held by the Constitutionalists), the French navy was able to spare only a small squadron of 10 ships under Counter-Admiral Jacques Félix Emmanuel Hamelin to blockade the city. That proved too small a force for Hamelin to succeed in this mission and so on 27 August he was replaced by Counter-Admiral des Rotours, then by Duperré, who arrived only on 17 September, with meagre reinforcements.

French troops besieging the fort of Trocadero

On 31 August the French infantry assaulted Fort de Trocadero and successfully captured it at the cost of 35 killed, 110 wounded (with 150 dead, 300 wounded, 1,100 captured among the garrison), turning its powerful guns towards Cádiz. On 20 September, Fort Sancti-Petri fell in its turn in a combined army–navy operation. On 23 September, the guns of the Sancti-Petri and Trocadero forts and of Duperré's fleet bombarded the town and on 28 the constitutionalists adjudged the town lost. Thus, the Cortes decided to dissolve itself, give back absolute power to Ferdinand VII and hand him over to the French. On 30 September Cádiz surrendered and on 3 October more than 4,600 French troops landed at its port. The French army fired its last shots in Spain at the start of November. On 5 November, the Duke of Angoulême left Madrid and re-entered France on 23 November, leaving behind an occupying force of 45,000 men under the command of Bourmont. Spain was then progressively evacuated, but the French withdrawal was fully completed only in 1828.

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