Adair, Sir William Thompson (1850–1931), Royal Marine and UVF officer, was born 21 June 1850 (son of Gen. Sir Charles William Adair, KCB) and educated at Cheltenham College. He entered (1867) the Royal Marines – following his father, grandfather, and great-uncle – in the light infantry. He taught fortification as an instructor at the Royal Military College (1886–90) and professor at the Royal Naval College (1890–95), and received the Queen's Medal with clasp for his work as special service officer and staff officer in South Africa (1900). Adair then served as assistant (1900–05) and deputy (1907–11) adjutant-general of the Royal Marines, and was made a KCB (1909). He then took up residence at Loughanmore, Co. Antrim. In 1912 he was promoted to general and became a JP and DL for Co. Antrim.
Although a magistrate and a serving officer, he also became commander of the Antrim Division of the UVF. On 20 January 1914 he and three of his regimental commanders saw Sir Edward Carson (qv) and James Craig (qv) to convey the dissatisfaction of the Antrim UVF with the state of provision of arms and the treatment of the Antrim force in particular. The subsequent landing of arms (24–5 April 1914) was made in Adair's divisional area, at Larne, Co. Antrim, a suitable place for dispersal throughout Ulster. The reception of the arms was thus his responsibility, and required ‘every form of conveyance, including motor-cars, a few motor-lorries, farm waggons and carts, pack-horses and bicycles . . . even a steam-roller and trailer and perambulators’ (Wilfrid Spender (qv), foreword to Crawford, p. x). The results, however, did not decisively improve Antrim's readiness for action. When, three months later, Adair ordered north Antrim units to supply 1,000 men for service elsewhere, the captain in charge refused to obey, on the grounds of logistic difficulty and the weakness of the UVF in north Antrim.
The outbreak of war in Europe in August diverted or dissipated the energies and organisation of the UVF, and after his retirement (1915) Adair was high sheriff of Co. Antrim (1916) and first honorary colonel-commandant of the Chatham division, Royal Marines (1923–5). A Knight of Grace of the Order of St John of Jerusalem, he died 29 December 1931. He married first (1880) Rose Naylor (d. 1903); secondly (1905) Angela Plowes; there were no children.