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Sir Denzil Macarthur-Onslow (1904–1984)

by Dayton McCarthy

This article was published:

Denzil Macarthur-Onslow, 1964

Denzil Macarthur-Onslow, 1964

National Archives of Australia, A1200, L46333

Sir Denzil Macarthur-Onslow (1904-1984), army officer, businessman and grazier, was born on 5 March 1904 at Whataupoko, Poverty Bay, New Zealand, eldest of four children of New South Wales-born parents Francis Arthur Macarthur-Onslow, sheep-farmer, and his wife Sylvia Raymond, née Chisholm.  A descendant of John Macarthur, Denzil was raised on a family property at Menangle, New South Wales.  He was educated at Tudor House, Moss Vale, and The King’s School, Parramatta.  Leaving school in 1922, he began his long association with the military on 20 August 1924, when he was commissioned as a lieutenant in the Militia.  Interested in flying, that year he joined the Royal Aero Club of New South Wales and became a partner in Light Aircraft Pty Ltd, a manufacturer of parachutes.  In the 1920s he followed a number of eclectic pursuits, travelling abroad to study both the latest dairying techniques and aviation engineering.  He was a quietly spoken teetotaller and non-smoker.  On 5 July 1927 at Holy Trinity Church of England, Brompton, London, he married Elinor Margaret Caldwell.

Having risen to captain, in 1935-38 Macarthur-Onslow was a general staff officer with the 1st Cavalry Division.  Promoted to major in October 1939, he volunteered for the Australian Imperial Force, joining the 6th Division Reconnaissance (Cavalry) Regiment.  In January 1940 he sailed for the Middle East and, after training in Egypt, took his squadron to Cyrenaica, Libya.  During attacks on Bardia in January 1941, the squadron captured two thousand prisoners and held an enemy post until reinforcements arrived.  For this action, Macarthur-Onslow was mentioned in despatches and in May was awarded the Distinguished Service Order.  Promoted to lieutenant colonel and placed in command of the 6th Division Cavalry Regiment on 11 June, he participated in the Syrian campaign in July.  Regarded by his men as a ‘cracker bloke’, he raised an equestrian unit, known as the ‘Kelly Gang’, which operated in mountain country, and he led two armoured squadrons during the capture of Merdjayoun.  He was again mentioned in despatches.  Returning to Australia in March 1942, Macarthur-Onslow was promoted to temporary brigadier.  He commanded the 1st Armoured Brigade from July until January 1943 when he took command of the 4th Armoured Brigade.  Although he was mostly based in Australia for the remainder of the war, he visited elements of his brigade in New Guinea on numerous occasions.

Taking leave without pay in July 1943, Macarthur-Onslow contested the seat of Eden-Monaro for the Liberal Democratic Party in the Federal election in August.  Unsuccessful, he returned to active duty.  He undertook parachute training and in October 1944 reputedly became the only Australian army officer to be a fully qualified parachutist.  On relinquishing command of the 4th Armoured Brigade in March 1946, he transferred to the Reserve of Officers with the honorary rank of brigadier.  At the Federal elections in 1946 and 1949 he failed to win Eden-Monaro for the Liberal Party of Australia.

Macarthur-Onslow returned to his property, Mount Gilead, Menangle, and established in Sydney Denzil Macarthur-Onslow Pty Ltd, a manufacturer of pastry-cook supplies.  Retaining an association with the military, on 14 November 1947 he took command of the 1st Armoured Brigade, Citizen Military Forces.  He was promoted to brigadier in January 1949.  Having divorced his wife, he married Dorothy Wolseley Conagher, née Scott, a medical practitioner, on 25 September 1950 at the assistant district registrar’s office, Petersham, Sydney.  He was appointed CBE in 1951 and relinquished command of the 1st Armoured Brigade on 31 August 1953.  From 16 August 1954 he commanded the 2nd Australian Division and was promoted to major general a year later.  On 1 December 1958 he was appointed CMF member on the Military Board, which made him the highest ranking CMF officer in the country and the only one to sit on the army’s decision-making body.

On 30 November 1960 Macarthur-Onslow returned to the Reserve of Officers.  He was knighted in 1964.  A long-time member of the Big Brother Movement, he served as president (1966-80).  He maintained his business interests, sitting on a number of company boards including those of Clyde Industries Ltd, Meggitt Ltd, Pettiford Holdings Ltd, Philips Industries Holdings Ltd and Total Australia Ltd.  President (1966-69) of the Australian Club, Sydney, he was also a member of the Royal Sydney Golf and Australasian Pioneers’ clubs.  Survived by his wife and their son and daughter and three sons and a daughter of his first marriage, Sir Denzil died on 30 November 1984 at Castle Hill and was cremated with Anglican rites.

Select Bibliography

  • G. Long, Greece, Crete and Syria, 1962
  • R. N. L. Hopkins, Australian Armour, 1978
  • D. McCarthy, The Once and Future Army, 2003
  • People (Sydney), 11 April 1951, p 22
  • B883, item NX135 (National Archives of Australia)

Citation details

Dayton McCarthy, 'Macarthur-Onslow, Sir Denzil (1904–1984)', Australian Dictionary of Biography, National Centre of Biography, Australian National University,, published first in hardcopy 2012, accessed online 24 June 2024.

This article was published in hardcopy in Australian Dictionary of Biography, Volume 18, (Melbourne University Press), 2012

View the front pages for Volume 18

© Copyright Australian Dictionary of Biography, 2006-2024

Denzil Macarthur-Onslow, 1964

Denzil Macarthur-Onslow, 1964

National Archives of Australia, A1200, L46333

Life Summary [details]


5 March, 1904
Whataupoko, Poverty Bay, New Zealand


30 December, 1984 (aged 80)
Castle Hill, Sydney, New South Wales, Australia

Cultural Heritage

Includes subject's nationality; their parents' nationality; the countries in which they spent a significant part of their childhood, and their self-identity.

Religious Influence

Includes the religion in which subjects were raised, have chosen themselves, attendance at religious schools and/or religious funeral rites; Atheism and Agnosticism have been included.