rocket, consisted of twenty 8-inch mortars carried on block-trail carriages of the pattern reintroduced in 1860, and drawn by teams driven by postilions instead of by wagoners on foot, as previously was the custom with field artillery. Attached to the equipment was a battery of field guns and wagons with entrenching tools, &c. The object was in the event of the enemy effecting a landing to harass him at night by a continuous shell fire, preparatory to an attack by the three arms at daybreak. Details are given by Douglas in his ‘Defence of England’ (London, 1860), pp. 27–9. Douglas became a captain in the royal artillery in 1804, but his services being required at the Royal Military College, he was placed on half-pay, and subsequently retired from the artillery and appointed to a majority in the 1st battalion of the army of reserve on 12 Oct. 1804, and the next day placed on half-pay of the York rangers, a corps reorganised for special service in the suppression of the African slave trade, which was then reduced. It was distinct from the later royal York rangers. On the retired list of that corps Douglas continued until promoted to the rank of major-general.
The Military College had been recently founded, the senior department being at High Wycombe. Douglas was in 1804 appointed commandant of the senior department, and afterwards ‘inspector-general of instructions,’ an office which he retained until its abolition in 1820 (Parl. Papers; Accts. and Papers, 1810, vol. ix.; Rep. Select Comm. 1854–5, xii. 157–8). Douglas improved and extended the system of instruction, and raised the disciplinary tone of the establishment. Among the pupils during his tenure of command were Philip Bainbrigge, Henry Hardinge, William Maynard Gomm, and many other well-known officers of the Peninsular epoch. He became brevet lieutenant-colonel 31 Dec. 1806.
In 1808 the reduction in the number of officers at the senior department led Douglas to seek active employment. He was appointed assistant quartermaster-general in Spain, and sent out with despatches to Sir John Moore. He joined the retreating army in December at Benevente, and was present at the battle of Corunna, 18 Jan. 1809. In July 1809 he accompanied the Walcheren expedition in the same capacity, and took an active part in the artillery attack on Flushing. The journal of the expedition, signed by the quartermaster-general, Sir Robert Brownrigg, and appended to the report of the parliamentary commissioners, is from his pen (see ‘Scheldt Papers,’ in Accounts and Papers, 1810). The same year he succeeded to the baronetcy on the death of his elder half-brother, Vice-admiral Sir William Henry Douglas, second baronet, on 23 May 1809. Douglas resumed his college duties, and on 2 July 1811 the reflecting circle or semicircle known by his name was patented by him, and described by Cary the optician in Tilloch's ‘Philosophical Magazine,’ July–December, 1811, pp. 186–7. The same year Douglas was selected by Lord Liverpool to proceed to the north of Spain to inspect and report on the state of the Spanish armies in Galicia and Asturias, and on the military resources of that part of the country then not wholly occupied by the French, and to report in what way these resources, regular and irregular, including the guerilla system, which had become very formidable, should be encouraged and extended (Fullom, Life of Douglas, pp. 235–6). After conferring with Lord Wellington he proceeded on his mission, and was present at the operations on the Orbigo and Esta, in the combined naval and military operations of the Spaniards and a British naval squadron under Sir Home Popham the younger, on the north coast of Spain in the early part of 1812, in the attack on and reduction of Lequertio, siege of Astorga, operations on the Douro, siege of Zamorra and attack on the ports of the Douro (see Fullom, ib. pp. 112–217; Douglas, Modern Fortifications, pp. 235–47; Gurwood, Well. Desp. vol. v.; Napier, Hist. Penins. War, bks. xvii–xix.; James, Naval Hist. vol. v.) He joined the army on the advance to Burgos at the end of August 1812, and appears to have predicted the failure of the siege (Fullom, p. 206), but did not await the result, the home government having recalled him from the mission, ‘which you have executed to the perfect satisfaction of his majesty's government,’ in consequence of ‘the repeated and earnest representations of the supreme board of the Royal Military College in regard to the detriment which the establishment suffers during your absence’ (Despatch from Lord Liverpool, ib. p. 218). Douglas became brevet colonel 4 June 1814, and major-general 19 July 1821.
In 1816 Douglas brought out the first edition of his work on military bridges, which is said to have furnished Telford with the idea of the suspension principle in bridge construction. It was compiled as a manuscript text-book for the use of the Military College, and was submitted to the authorities in 1808, together with a plan of organisation for a corps of pontooners. In 1819 he published his treatise on Carnot's system of fortification; and in 1820 the first edition of his treatise on naval gunnery. The preface to the latter states that observations made and
