The Admiralty Compass Observatory Collection comprises correspondence papers and reports, 1842 -1950 transferred from the Public Record Office, The National Archives, Kew in 1983, Papers from the Scientific and Technical Review Section (S&T) 1890 - 1970 acquired in 1993 and 1996 also from the Public Record Office, The National Archives, Kew. Further to these series the collection is divided into twelve sections of material deposited from the National Archives, Kew, in 1983. These are HM Ships Compass Bearings 1842-1918, Swing Books 1904-1930, Admiralty Compass Department D Series, N Series 1870 - 1980, R series 1826-1946, Reports 1956 - 1962, Compass Department Examination of Instruments, Compass Observations and Experiments 1842 - 1933, Magnetic Elements of HM Ships 1864 - 1918, further correspondence and papers 1873 - 1914, handbooks and miscellaneous material 1842 - 1953, manuscripts removed from the Compass Department Library and catalogues, inventories and indexes.

Administrative / biographical background
The Admiralty Compass Observatory (ACO) formed in March 1842 to improve the Mariners compass, following the recommendations of the Compass Committee, set up in July 1837. This committee comprised Captain (later Rear- Admiral Sir) Francis Beaufort (1774- 1857), Captain (later Rear- Admiral Sir) James Clark Ross (1800 - 1862), Major (later General Sir) Edward Sabine (1788-1883), Samuel Hunter Christie (1784- 1865), Captain Thomas Best Jarvis and Commander Edward John Johnson (1794-1853). All bar Jarvis were fellows of the Royal Society. The committee examined specimens and conducted experiments and in April 1838 it stressed the need for accurate information on VARIATION. The committee perfected what became the Pattern 1 Admiralty Standard Compass (in service from 1840- 1944), being adopted by foreign navies. In March 1842 the committee submitted a set of ?Practical Rules?, which went through eleven editions up to 1889. Captain Johnson was appointed to implement the findings of the committee. Johnson initially was the sole member of the new branch and was responsible for instructing officers of the fleet in the operation of swinging ship, assisting the Master Shipwrights in determining the most advantageous position for the pillar, examining and testing the new Standard Compasses and implementing the Practical Rules. In 1845, a set of ?safe distance rules? was published also known to many as CD pamphlet 11. In 1855, Commander Frederick Evans was appointed to the ACO when iron was being more widely used in ship construction and deviations of the compass where increasing. The status of the Compass Department rose rapidly after the publication of Evans and Archibald Smith produced a number of papers for the Royal Society, British Association and other learned bodies, including the publication of a number of manuals at advanced and popular levels. The papers dealt with the theory of the causes of magnetic deviation, its analysis and practical application. Evans won the department at the International Exhibition of 1862 for his effort in designing a binnacle to correct quadrantal deviation. In the five years up to 1860, the Liverpool Compass Committee produced three excellent reports on the subject of ships magnetism and the management of their compasses, tackling the problem of heeling error and the adoption of a ?Flinders bar?. In 1869, the Compass Department was moved to Deptford and an office created in London. In 1869 Rear Admiral Ryder proposed that every ship should have the compass fitted on her bridge. Sir William Thompson?s patents of 1876-9 greatly improved the azimuth device, which he invented. In 1868, Lieutenant E. W. Creak was appointed Assistant Superintendent of Compasses and Superintendent in 1887. In the 1870?s the binnacle for the first time provides a simple means of adjustment to meet the inevitable changes in deviation. Electricity when introduced, posed a threat to the stability of compass readings. In 1881, the navy installed a two-wire system into HM ships leaving the dynamo as a remaining principal cause of disturbance. Mayes subsequently conducted test in 1884, in the troopship EUPHRATES. ACO moved to Ditton Park, Slough in 1917, costing the Admiralty £20,000. In 1971 the ACO was absorbed into the Admiralty Surface Weapons Establishment (ASWE) as its navigation division. For further information about the history of the ACO refer to: Fanning, A. E. Steady As She Goes: A History of the Compass Department of the Admiralty, 1986, HMSO.