20th Deccan Horse
- 1790 raised as Asif Sah's Irregular Cavalry under the Colours of the Nizam of Hyderabad in Berar
- 1801 became the Nizam's Contingent
- 1816 became 1st Reformed Horse (Nawab Jalal-ul-Daula's)
- 1826 became 1st Regiment, Nizam's Cavalry
- 1854 became the 1st Cavalry, Hyderabad Contingent
- 1890 became the 1st Lancers, Hyderabad Contingent
- 1903 became the 20th Deccan Horse
- 1922 amalgamated with the 29th Lancers (Deccan Horse) to become the Royal Deccan Horse (9th Horse)
- 1947 allocated to India on Partition
- 1950 became The Deccan Horse (9 Horse)
First World War
Regimental History: The Royal Deccan Horse In The Great War by Lieutenant-Colonel E. Tennant 1939. Available at the British Library, and in a reprint edition, which in turn is available as an online book on the Ancestry owned pay website fold3, see below.
The regiment served on the Western Front, including taking part in a futile counter attack at Festubert in December 1914, and taking part in the Battle of Bazentin Ridge, part of the attack on High Wood in July 1916.
- Deccan Horse indiapicks.com
- 9th Royal Deccan Horse Wikipedia
- Ist Lancers, Hyderabad Contingent fotw.fivestarflags.com
- "With marigold, ‘India Remembers’ flowers on centenary of WWI Indian cavalry charge" by Manimugdha S Sharma July 14, 2016 Times of India.
Historical books online
- History of the Thirtieth Lancers Gordons Horse by Major E A W Stotherd 1911 is available as a pdf to download, Digital Library of India, or as a mirror edition on Archive.org. This regiment was previously called the 4th Lancers, Hyderabad Contingent. The preface states that a great deal of information will be found about the other three regiments of the Hyderabad Contingent Cavalry, as in many despatches they seem to have been regarded as one large corps.
- Illustration: "A Jemadar of the 20th Deccan Horse", near the front of the book Southern India Painted by Lady Lawler, Described by F E Penny 1914 Archive.org
- The Royal Deccan Horse In The Great War is available in a reprint edition, which in turn is available as an online book on the Ancestry owned pay website fold3 (located in World War II/Military Books/Britain, under letter T).
- The Royal Deccan Horse In The Great War Naval & Military Press
- Broomfield, Steven. Captain Charles Alexander Chandos Mackenzie - 20th Deccan Horse - kia Great War Forum 26 February 2016. Retrieved 27 September 2018.