Service in Malta and Sicily

On 1 March 1805 Jones was promoted second captain, and soon after embarked at Portsmouth with the expedition under Sir James Craig. After some months' cruising the troops were disembarked in July at Malta, where Jones did garrison duty until the autumn. He then accompanied the expedition to Naples, and was detached with the commanding engineer to Calabria to retrench a position at Sapri for covering a re-embarkation. From Naples the troops sailed for Sicily, and, on the dethronement of the king, garrisoned Messina and Melazzo. Jones was employed under Major Lefebure in constructing defence works. In spring 1806 Jones reported, for the king of Naples, on the forts, harbours, and military condition of Sicily. His work was commended by the Neapolitan government and by Sir John Moore. In June 1806 Jones embarked at Messina with a force under Sir John Stuart, which landed in the Bay of St Euphemia. He was present at the British victory of Maida (4 July), and marched with an advanced corps under General Oswald to sweep off the French detachments between Monteleone and Reggio, and to reduce Scylla Castle. The castle was so ably defended that its capture required the formalities of a siege. Jones successfully directed the attack, and after its capture persuaded Stuart to retain and strengthen it instead of blowing it up. Jones did this so well that it was held until February 1808, proving during that time a bar to the invasion of Sicily. When it was reduced to ruins by the French, the garrison was withdrawn in boats, without the loss of a single man, by means of a covered gallery constructed by Jones. He always considered the retention of Scylla the most meritorious achievement of his career. In December 1806, having visited Algiers en route, Jones returned to England, and on 1 January 1807 he was appointed adjutant at Woolwich, the headquarters of the Royal Military Artificers. The war necessitated the augmentation of the local and independent companies of engineer workmen, and Jones was occupied until 1808 in reorganizing them into one regular corps.

The Peninsular War

Following the Spanish insurrection against the French, and Spanish requests to Britain for assistance, in July 1808 Jones was selected to serve as one of the two assistant commissioners under General Leith, appointed military and semi-diplomatic agent to the juntas of northern Spain. Jones was attached to the army of the marqués de La Romana, and gained a great affection for its commander. Towards the end of the year Leith was ordered to take command of a brigade and to select an officer to succeed him as commissioner. Leith offered to appoint Jones, but he declined, though the high pay was tempting, on the ground that his youth and want of rank would deprive his advice of its proper weight, and he asked instead to join the army. Leith appointed him his acting aide-de-camp. Jones continued in this capacity until after the skirmish before Lugo, when he was ordered to assist in blowing up the bridge over the Tamboya, and was employed with his own corps during the retreat to Corunna. On his arrival in England he resumed his staff appointment at Woolwich, and on 24 June 1809 was promoted first captain. On 9 July he was appointed brigade major to the engineers under Brigadier-General Fyers to accompany the disastrous expedition under the earl of Chatham to the Dutch island of Walcheren, at the mouth of the Scheldt.

Jones acted throughout the operations in Zeeland as chief of the engineers' staff, and carried out the arrangements for the attack of Rammekins and Flushing. After the capitulation of Flushing, Jones remained until the defences had been repaired and strengthened, and then returned to England, 'bursting with feelings of rage and indignation' (Military Autobiography, 51). In his autobiography he insisted that the Walcheren expedition could have succeeded if properly commanded, but failed through Chatham's 'ignorance, incapacity, and indolence' (ibid., 43). Jones was appointed to command the engineers in the northern district.

In March 1810 Jones was ordered to embark for Lisbon, where he was employed under Colonel Richard Fletcher on the lines of Torres Vedras, the crucial defence works, ordered by Wellington, which secured Lisbon and the British bridgehead in Iberia and enabled the later British victories there. In June Fletcher joined the army headquarters at Celerico and Jones was appointed commanding engineer in the south of Portugal, entrusted with completion of the works against the threatened French invasion under Massena. The arrangements for manning the works had been so well made by Jones that they were quickly occupied.

On 17 November 1810 Jones was appointed brigade major of engineers in the Peninsula and was attached to the headquarters' staff, the details of the engineers' service in all parts of the Peninsula passing through his hands. He held the appointment until May 1812, and served at all the sieges of that period. For his conduct during the operations against Ciudad Rodrigo he was particularly mentioned by Wellington in his dispatches, and was promoted brevet major on 6 February 1812. At the siege of Badajoz, Sir Richard Fletcher, the commanding engineer, was wounded, but at Wellington's wish retained his command, and the active duties devolved on Jones, his staff officer. In the assault on Fort Picuriaz, Jones saved the life of Captain Holloway of the engineers, who had been shot down on the parapet and fell onto the fraise. For his services at the siege Jones was promoted on 27 April 1812 brevet lieutenant-colonel, and resigned his appointment as brigade major.

When it was decided to carry on operations on the eastern coast of Spain, Jones was appointed commanding engineer under General Frederick Maitland, and sailed from Lisbon at the beginning of June. On the disembarkation of the troops at Alicante, Jones received a staff appointment as assistant quartermaster-general, there being already an engineer officer senior to himself in command of the engineers. Owing to differences between the commanders of the allied forces, Jones was sent on a special mission to Madrid to explain the situation to Wellington. Travelling by night and avoiding roads, Jones reached Madrid safely and was warmly received by Wellington, who kept Jones to accompany him to the siege of Burgos. During the siege, Jones was ordered to signal to Wellington by holding up his hat when the arrangements for exploding a mine and making a lodgement were complete. As the signal was not acknowledged, Jones repeated it until the French noticed him and shot him through his ankle. He with difficulty rolled himself into the parallel, but he ordered the mine to be fired, and the operations entrusted to him were successfully carried out before he left the field. Jones was delirious for ten days, and as soon as he could be moved Wellington sent him to Lisbon in the only spring wagon at headquarters. The sufferings of this two months' journey severely tried his strength, and he remained in Lisbon until April 1813, when he was sent to England. Eighteen months of severe suffering followed. Indignant at the unnecessary loss of life 'merely for want of the most simple means for attacking fortresses being with the army' (Military Autobiography, 107), he published Journal of Sieges Carried on by the Allies in Spain in 1810, 1811, and 1812 (2 vols., 1814). In this work he fearlessly exposed the deficiencies of the engineer service, blaming the ignorance and military incapacity of the Board of Ordnance and its advisers. His strictures offended the dispensers of patronage. Wellington, however, although the book was published without his sanction and criticized his siege proceedings, praised it, and remained Jones's friend.

From the Napoleonic War onward, British policy was to exclude France from the Low Countries and the naval resources of Antwerp and the Scheldt, and to prevent future French expansion and increased naval strength. Crucial to this were the British-promoted, Orange-ruled kingdom of the United Netherlands and its Belgian fortifications, partly British financed, as a barrier against France. In 1814 Jones visited the Netherlands and examined the principal fortresses. Wellington appointed him, with Brigadier-General Alexander Bryce and another engineer officer, to report on the system of defence for the new United Netherlands. The commissioners arrived in Brussels on 21 March 1815. On 4 June 1815 Jones was made a CB. On Wellington's appointment to the command in the Netherlands, Jones accompanied him round some of the principal points of defence. At the end of August the reports of the commission were taken to Paris by Bryce and Jones and submitted to Wellington, with whom all details were settled by March 1816, when the commission was broken up. Jones was then selected to be Wellington's medium of communication with the Netherlands' government for the furtherance of the objects of the report. In the previous December Jones, with Colonel Williamson, Royal Artillery, acting as commissioners of the allied sovereigns, prevented the fortress of Charlemont from falling into Prussian hands. The commissioners took possession of Landrecy for the allies and returned to Paris in January 1816.

Inspector of fortifications

On 20 April 1816 Jones married, in London, Catherine Maria (d. 1 Dec 1859), daughter of Effingham Lawrence of New York. They had three sons and a daughter. In November 1816 a convention founded on the treaty of Paris was signed between England and the Netherlands, empowering Wellington to spend a fund of £6.5 million in constructing fortifications and to delegate his powers to inspectors. The duke named Jones sole inspector, and insisted on his choice despite strong pressure on behalf of a superior officer. Jones's duty was to make periodical inspections of each fortress, superintend the execution of approved plans, sanction modifications, and check expenditure. Wellington usually made two inspections of some weeks annually, when he was always attended by Jones alone, and became intimate with him. On the return to England of the army of occupation Jones, promoted regimental lieutenant-colonel on 11 November 1816, was appointed to the command of the Royal Engineers and Royal Sappers and Miners at Woolwich, with a range of responsibilities including the gunpowder factories at Waltham Abbey and elsewhere, while still acting as inspector in the Netherlands. He also served on varied military committees. In 1823 he was sent by Wellington to the Ionian Islands to confer with the high commissioner, Sir Thomas Maitland, on the defences of Corfu. His plans were approved and gradually carried out. On 27 May 1825 he was appointed aide-de-camp to the king, with the rank of colonel in the army. On 19 August 1830 Wellington sent him on a special mission to the Netherlands with a view to any military arrangements advisable on account of the July revolution in France. At Ghent, Jones heard of the Brussels rising, went to William I of the Netherlands at The Hague, and at William's request joined the Dutch army and the prince of Orange at Antwerp. On his advice the prince went to Brussels, where he had a good military position and sufficient force to maintain himself. Two hours after Jones had left Brussels for London to report on his mission, the prince retired to The Hague, thus abandoning his advantages and determining the subsequent course of the revolution. Jones was shocked at the Dutch loss of the fortifications and the sudden collapse of the barrier strategy, but his own role was questionable and Wellington was displeased. From 1820, when he inherited a considerable landed property, Jones repeatedly asked Wellington for a baronetcy. Finally, on Wellington's recommendation but through the whig prime minister, Grey, on 30 September 1831 Jones was made a baronet for his services in the Netherlands. Wellington suggested a castle with the word ‘Netherlands’ as an addition to his armorial bearings. According to John Wade's Extraordinary Black Book (1832) Jones was paid £1107 per annum and a £300 wound pension. He was consulted by Palmerston on the Netherlands and the fortifications there. From 1835 to 1838 Jones's health compelled him to live in a southern climate. He was promoted major-general on 10 January 1837, and on 19 July 1838 he was made a KCB.

In the summer of 1839 Jones was requested by the master-general of the ordnance to revise and systematize the plans for the defence of British coasts and harbours against possible French attack using steam vessels, and in the spring of 1840 was a member of a commission on colonial defences. He next undertook at government request a general scheme of defence for Great Britain, in consultation with Wellington. Following anxiety at a possible French attack, in early October 1840 he visited Gibraltar to report on the defences, remaining there as major-general on the staff until June 1841, when he returned to England. His proposals for the improvement of the Gibraltar defences were approved and gradually carried out.

Writings

Jones was the author of a short account of Sir John Stuart's campaign in Sicily, published in 1808. His Account of the war in Spain and Portugal and in the south of France, from 1808, to 1814, inclusive (2 vols., 1818), written partly in response to French accounts which he believed distorted, claimed the importance of the guerrilla war had been much overrated. He printed in 1829 for private circulation Memoranda Relative to the Lines Thrown up to Cover Lisbon in 1810, later published in the Professional Papers of the Corps of Royal Engineers. A third edition of the Journal of Sieges, in 3 volumes, edited and augmented by his brother Sir Harry David Jones, who incorporated the Torres Vedras memoranda, was published in 1843. Jones's 'Reports relating to the re-establishment of the fortresses in the Netherlands from 1814 to 1830' were, by permission of the secretary for war, edited by Sir Harry Jones and printed for circulation among Royal Engineers officers. Jones's publications continue to be valuable sources, still used by historians.

Jones was considered among the first military engineers of his day. He possessed talents of the highest order: great mathematical knowledge, coupled with sound judgement. He was present at six sieges, at five as brigade major, and his intimate knowledge gave great value to his publications on them. His reputation as a military engineer was not confined to Britain.

From the autumn of 1842 to February 1843 Jones wrote for his family his military autobiography. He died, after a day's illness, on 26 February 1843 at his residence at Pittville, Cheltenham, Gloucestershire. Royal Engineers officers subscribed for a memorial statue by William Behnes, in St Paul's Cathedral south transept. His son Sir Willoughby edited Jones's Military Autobiography (1853), 'twelve copies only printed for family perusal'. Jones's eldest son, Sir Lawrence, second baronet (b. 10 Jan 1817), was murdered by brigands on 7 November 1845 when travelling between Macri and Smyrna, and was succeeded in the baronetcy by his brother Willoughby (1820–1884), whose eldest son, Lawrence (1857–1954), was the fourth baronet.