of time: notable among these young assistants were Paul Sandby (born 1731), later renowned for his watercolour landscapes, and a seventeen-year-old David Dundas (born 1735), later Commander-in-Chief of the armed forces. Eventually there were six teams conducting surveys by traverses of the country with the objects to the side of the line recorded by sketches and compass directions. The Highlands were covered by 1752, but the survey was extended to the lowlands for another three years, until 1755, when most of the engineer surveyors were posted to war stations. In the introduction to the 1885 account of the measurement of the Hounslow baseline Roy writes that the map remained "in an unfinished state ... and is to be considered as a magnificent military sketch rather than a very accurate map of a country ... (and) it would have been completed, and many of its imperfections no doubt remedied, but for the breaking out of war in 1755." The eighty-four original field sheets and the thirty-eight divisions of the "fair-protraction"are held in the British Museum together with a small index map and a reduced map of the whole country in a single sheet published as "the King's map". It is now possible to view the map online. Military appointments Throughout the Survey of Scotland, Roy was a civilian assistant to David Watson the deputy quartermaster-general, but in 1755 the survey was terminated by the outbreak of the Seven Years' War with France and the consequent redeployment of personnel to more pressing posts in both the regular army and the Board of Ordnance. In the same year the engineers of the board were formed into the Corps of Engineers. The board officers were members of both structures, for they would be deployed with the army regiments for specialist duties. In 1776 Roy was commissioned as a lieutenant in the 53rd Foot, a new regiment formed in 1755. At the same time he was appointed as a practitioner-engineer, the lowest rank in the Board of Ordnance survey department, and ensign in the Corps of Engineers. Thereafter Roy was promoted steadily, and rapidly, in both structures, but his army rank was always greater than his board rank. For example, he was lieutenant-colonel in the army by 1762 and director and lieutenant-colonel of the Engineers in 1783. He is best known by his army rank of major-general, which he attained in 1781. From 1786 to