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 a small index map attached. Its revision and completion were contemplated in 1755, but prevented by the outbreak of war. At a later date the map was reduced by Watson and Roy, engraved in a single sheet by T. Chievos, and published as the king's map. Roy's love of archæology showed itself in the insertion of the names of Roman places and camps.

On 23 Dec. 1755 Roy, who had already received a commission in the 4th King's Own foot, was made a practitioner-engineer. A serious alarm of a French invasion caused the removal from Scotland of Watson and his two assistants—Roy and David Dundas (1735–1820) [q. v.]; the latter joined Roy in Scotland in 1752. They were now employed in making military reconnaissances of those parts of the country most exposed to attack. Roy's share mainly consisted of the coasts of Kent and Sussex. He was, however, so neat a draughtsman—as numerous drawings in the British Museum testify—that besides his own surveys, he frequently drew the maps of country surveyed by Watson and others. In 1757 Roy took part in the expedition against Rochefort under Sir John Mordaunt (1697–1780) [q. v.], and was present at the capture and demolition of the fortifications of the Isle d'Aix. He gave evidence before the general court-martial at the trial of Mordaunt.

On 17 March 1759 Roy was promoted to be sub-engineer and lieutenant, and on 10 Sept. the same year to be engineer and captain in the corps of engineers. Roy served under Lord George Sackville in Germany this year, and took part in the battle of Minden, 1 Aug. On 20 Aug. he was promoted in the infantry from captain-lieutenant of Brudenell's, or 4th foot, to be captain of a company in the corps of highlanders. In 1760 Roy gave evidence before the general court-martial at the trial of Lord George Sackville. During 1760 and 1761 Roy served in Germany as deputy quartermaster-general of the British force under the Marquis of Granby, and took part in all the operations in which that force was engaged. On 11 Nov. 1761 he was promoted major of foot, and appointed deputy quartermaster-general of the forces in South Britain. On 23 July 1762 he was promoted lieutenant-colonel in the army, returning to Germany to serve again under the Marquis of Granby as deputy quartermaster-general.

On the conclusion of peace in 1763 Roy was entrusted with a general survey of the whole island of Great Britain; but the scheme came to nothing. Roy went to Scotland in 1764, and collected material for his work on military antiquities.

On 19 July 1765 Roy was appointed by royal warrant to a new post, entitled surveyor-general of the coasts and engineer for making and directing military surveys in Great Britain. His new duties were in addition to those of deputy quartermaster-general to the forces and engineer-in-ordinary. In October he was sent to Dunkirk on special service, with an allowance of 3l. a day, to examine into the state of the demolitions which were being carried out under the treaties with France. Roy met at Dunkirk his colleagues, Colonels Desmaretz and Andrew Fraser. Their report upon the Mardyke channels, dated 15 Feb. 1766, and the plans of Dunkirk made by Fraser, are in the royal artillery library at Woolwich.

In 1766 Roy visited Ireland, and wrote ‘A General Description of the South Part of Ireland, or Observations during a Short Tour in Ireland,’ 1766. The work was not printed; the original manuscript is in the British Museum. In 1767 he became a fellow of the Royal Society of London, and he was also a fellow of the Society of Antiquaries.

In 1768 he seems to have visited Gibraltar, and next year he submitted to the master-general of the ordnance a report upon the defences of this fortress, with projects for their improvement. In September 1775 Roy visited Jersey and Guernsey to report on housing additional troops. On 29 Aug. 1777 he was promoted to be colonel in the army, and on 19 Oct. 1781 to be major-general. In 1782 Roy was examined by the public accounts commission on his experience in regard to expenditure in the last war in Germany when he was in charge of both the quartermaster-general's and the chief engineer's departments. On 1 Jan. 1783 Roy was appointed director and lieutenant-colonel of royal engineers, and shortly after was made a member of a committee on the defences of Chatham. On 16 Sept. Roy was promoted colonel in the royal engineers, and was appointed a member of the board on fortifications presided over by the Duke of Richmond. On 15 Nov. 1786 Roy became colonel of the 30th regiment of foot.

Roy occupied his leisure time in scientific and archæological pursuits. In 1778 he read a paper before the Royal Society, entitled ‘Experiments and Observations made in Britain in order to obtain a Rule for measuring Heights with the Barometer.’ It was published separately the same year. In 1783 Roy was employed by the English government to carry a series of triangles from London to Dover, and connect them with the triangulation already made between Paris