The position of the fortress on a long narrow isthmus of sand rendered it difficult to approach, and it was not only well supplied, but contained casemated barracks for a garrison of eight hundred men under General Camus.
The now-General Oswald effected a landing on 23 March and the enemy were driven out of their forward entrenchments at bayonet point by the 35th Regiment of Foot.
Large working parties were at once sent in and the entrenchment converted into a secure lodgement from which the British infantry and sharpshooters were so able to distress the artillery of the fort that it surrendered.
Major Thackeray sailed in July 1812 with the Anglo-Sicilian army under Lieutenant-General Frederick Maitland and landed at Alicante in August.
He took part in the operations of this army, which, after Maitland's resignation in October, was successively commanded by Generals Mackenzie, William Henry Clinton, Colin Campbell, and Sir John Murray, who arrived in February 1813.
In May 1813 he embarked with the army, fourteen thousand strong, with a powerful siege train and ample engineer stores, for Tarragona, where they disembarked in June.
Thackeray directed the siege operations, and by 8 June a practicable breach was made in Fort Royal, an outwork over four hundred yards in advance of the place.