until 1797, when he went to the West Indies, having been promoted to be first lieutenant on 18 June 1796. He took part, on 20 Aug. 1799, in the capture of Surinam under Sir Thomas Trigge. In 1801 he was aide-de-camp to Trigge at the capture of the Swedish West India island of St. Bartholomew on 21 March, the Dutch island of St. Martin on 24 March, the Danish islands of St. Thomas and St. John on 28 March, and of Santa Cruz on the 31st of that month.
On 18 April 1801 Thackeray was promoted to be second captain. He returned to England the following year, and in 1803 proceeded again to Gibraltar. He was promoted to be first captain on 1 March 1805, and returned to England. In February 1807 he was sent to Sicily, whence he proceeded with the expedition under Major-general McKenzie Fraser to Egypt, returning to Sicily in September. In 1809 Thackeray was commanding royal engineer with the force under Lieutenant-colonel Haviland Smith, detached by Sir John Stuart [q. v.] (when he made his expedition to the Bay of Naples) from Messina on 11 June to make a diversion by an attack on the castle of Scylla. The siege was directed by Thackeray with such skill that, although raised by a superior force of French, the castle was untenable, and had to be blown up.
In March 1810 Thackeray was sent from Messina by Sir John Stuart with an ample supply of engineer and artillery stores to join Colonel (afterwards General Sir) John Oswald [q. v.] in the Ionian Islands, to undertake the siege of the fortress of Santa Maura. Its position on a long narrow isthmus of sand rendered it difficult of approach, and the fortress was not only well supplied, but contained casemated barracks sufficient for its garrison of eight hundred men under General Camus. Oswald effected a landing on 23 March. From the situation of the place no enfilading batteries could be erected; but after the British direct batteries had opened fire the siege works were pushed gradually forward, until on 15 April Thackeray pointed out the necessity for carrying by assault an advanced entrenchment held by the enemy which would enable him to reconnoitre the approach to, and the position for, the breaching battery, and he proposed to turn this entrenchment when taken into an advanced parallel of the attack. The operation was carried out successfully; the enemy were driven out of the entrenchment at the point of the bayonet by Lieutenant-colonel Moore of the 35th regiment; large working parties were at once sent in, and, by Thackeray's judicious and indefatigable exertion, the entrenchment on the morning of the 16th was converted into a lodgment from which the attackers could not be driven by the fire of the enemy, while the British infantry and sharpshooters were able so greatly to distress the artillery of the place that in the course of the day, 16 April 1810, it surrendered. Thackeray was mentioned in general orders and in despatches. Oswald also wrote to thank him. Thackeray received on 19 May 1810 a brevet majority in special recognition of his services on this occasion.
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 Clinton, Campbell, and Sir John Murray, who arrived in February 1813. On 6 March Thackeray marched with the allied army from Alicante to attack Suchet, and was at the capture of Alcoy. He took part in the battle of Castalla on 13 April, when Suchet was defeated. On 31 May he embarked with the army, fourteen thousand strong, with a powerful siege train and ample engineer stores, for Tarragona, where they disembarked on 3 June. Thackeray directed the siege operations, and on 8 June a practicable breach was made in Fort Royal, an outwork over four hundred yards in advance of the place. Thackeray objected to an assault on this work before everything was ready for the construction of a parallel and advance from it. All was prepared on 11 June, and instructions were given for an assault after a vigorous bombardment. But Murray having received intelligence of a French advance counter-ordered the assault and raised the siege. For this he was afterwards tried by court-martial at Winchester, and found guilty of an error of judgment. Murray seems at the time of the siege to have blamed Thackeray for delay, for on the arrival of Lieutenant-general Lord William Bentinck to take command on 18 June, Thackeray wrote to him that an attempt had been made to attach blame to him on account of the termination of the siege of Tarragona, and requested Lord William as an act of justice to cause some investigation to be made into his conduct before Sir John Murray left, and while all the parties were present who could elucidate the matter. This letter was sent to Murray, who completely exone-
