As
Earl Grosvenor he joined the
Territorial Army in 1970, as a
trooper, family estate responsibilities having caused him to abandon a Regular Army career in the
9th/12th Lancers. After entering
RMA Sandhurst in 1973, he passed out as an
officer cadet and was commissioned a
second lieutenant in the
Territorial and Army Volunteer Reserve of the
Royal Armoured Corps (
Queen's Own Yeomanry) on 13 May 1973. He was promoted to
lieutenant on 13 May 1975 and to
captain on 1 July 1980. He was promoted to the acting rank of
major on 1 January 1985 and to the substantive rank on 22 December. Promoted to
lieutenant-colonel on 1 April 1992, he subsequently commanded the
North Irish Horse, the
Cheshire Yeomanry Squadron, founded by his ancestors, and the Queen's Own Yeomanry. He was promoted to
colonel on 31 December 1994 and was appointed
honorary colonel of the
7th Regt Army Air Corps (1 January 1996) and the Northumbrian Universities Officer Training Corps (30 November 1995). Promoted to
brigadier on 17 January 2000, he was also appointed Honorary Colonel of the
Royal Mercian and Lancastrian Yeomanry on 14 May 2001. He was also appointed Colonel-in-Chief of the Canadian
Royal Westminster Regiment, the
North Irish Horse, and as
Colonel Commandant Yeomanry. The Duke was
Grand Prior of the Priory of England of the
Military and Hospitaller Order of St Lazarus of Jerusalem, 1995–2001. In 2004, he was appointed to the new post of
Assistant Chief of the Defence Staff (Reserves and Cadets), with promotion in the rank of
major-general. In March 2007, having served in the
Ministry of Defence as Assistant CDS for four years, he handed over responsibility for 50,000 reservists and 138,000 cadets to Major General
Simon Lalor, in the wake of the
Eliot Spitzer prostitution scandal in which Westminster was also implicated. The Duke became
Deputy Commander Land Forces (Reserves) in May 2011. He retired from the Armed Forces in 2012.
Benevolent work for service personnel The Duke was President of the
BLESMA from 1992, and the Yeomanry Benevolent Fund from 2005, national Vice-President of the
Royal British Legion from 1993, and the Reserve Forces'
Ulysses Trust from 1995, the Not Forgotten Society from 2004, and Chairman of the Nuffield Trust for the Forces of the Crown from 1992, all until his death. He was Vice-President of the
Royal Engineers Music Foundation 1990–94. Work started on the £300 million project in April 2016, and was completed in 2018 to replace those at
Headley Court. The Duke remained actively involved in the project until his death. He was Vice-President of the
Royal United Services Institute from 1993 until 2012, President of
The Tank Museum, Bovington, from 2002, and a committee member of the
National Army Museum between 1988–1997 and from 2013 until his death. Quinn quotes the duke himself: 'In many ways I'm a perfect example of a person who is famous for being famous—I mean a sort of second-rate celebrity! I get invited to things not because I have achieved great things in life but I'm afraid just because I am a duke. I go along with it because what else is there for a duke to do? As I have said many times, we, the aristocracy, in practical terms, are an irrelevance in the modern world. We just cut ribbons, open supermarkets and look the part.' ==Educational interests==