21st Light Horse Regiment

It's first CO was Captain C. D. Fuller. Headquarters were at Albion Park but later were removed to Kogarah and during the latter part of World War One to Ashfield.

The badge was a horse rampant in a circle on which was the unit's title; above the circle was a crown and below it a scroll with the motto "Virtus in Arduis".

The 28th was classified as Corps Mounted Troops and was attached to 3rd Light Horse Brigade (7th, 9th and 11th Regiments). During the war years, Capt P. Connolly was temporarily in command. Lt Col S. J. Shillington, V.D. commanded from 1919 to 1926.

In the re-organisation of 1921, the unit became 21st Light Horse Regiment (Illawarra Light Horse). The unit's colour patch was a white triangle with a blue centre. There were a number of changes in sub-unit localities from 1921 to 1929, within the area bounded by Arncliffe, Milton and Moss Vale.

The Regiment's Guidon received in 1928 bore the honorary distinction "South Africa, 1899-1902" but no World War One honours as there was no 21st Light Horse in the A.I.F.

However, in 1936, the following distinctions were approved to be borne on the Guidons of the several regiments which had no A.I.F. "parent": ANZAC, GALLIPOLI, 1915; EGYPT 1915-17; PALESTINE, 1917-18.

Amalgamation with 1st Light Horse Regiment (NSW Lancers) occurred in July 1929, the composite regiment being 1st/21st Light Horse Regiment (New South Wales Lancers). Four troops of 21st were disbanded, Mittagong troop was transferred to 7th and four troops were retained in 1st/21st.

New South Wales Lancers badges, with the designation, 1st/21st, were used.

On 3rd June, 1935, the title "Royal" was bestowed on the NSW Lancers so the unit's designation became 1st/21st Light Horse Regiment (Royal New South Wales Lancers). Then in November 1936, the Regiment was motorized and became 1st Light Horse (Machine Gun) Regiment. The number 21 was then linked with 7th which thus became known as 7th/21st. At the same time, Nowra and Kangaroo Valley Troops which had been part of 1st/21st were transferred to 7th/21st.

The 21st was reformed as a separate unit, 21st Light Horse Regiment (Riverina Horse), in July 1937, with Headquarters in Wagga Wagga. The other sub-unit locations were:
- HQ Sqn: Cootamundra, Stockingbingal, Sydney
- "A" Sqn: Narrandera, Griffith, Barellan
- "B" Sqn: Holbrook, Urana, Culcairn
- "C" Sqn: Tumbarumba, Gundagai, Tarcutta

The 1st became Divisional Troops and

4th Cavalry Brigade now comprised
- 6th,
- 7th and
- 21st Regiments.

The badge ensign adopted by 21st was that of Illawarra Light Horse but with the new designation, "Riverina Horse", and white metal was used instead of brass.

During the early part of World War Two, there were considerable changes of personnel as many left to join the A.I.F. and others were taken in to fill the gaps in the Regiment. At the end of September 1941, the 21st was placed on full-time duty and in December 1941, it was mechanized and re-designated 2nd Divisional Reconnaissance Battalion, which title was changed shortly afterwards to 21st Reconnaissance Battalion and again in September 1942, to 21st Australian Cavalry Regiment (A.I.F.)

It was transferred from 1st Cavalry Division in December 1941 and its subsequent service, partly in New South Wales and partly in Queensland, was successively with 2 Aust. Div., 1Aust. Div., 3 Aust. Div., 2 Aust. Corps, 3 Aust Armoured Div. In May 1943 came the order to disband it and form the personnel into five carrier companies.

As it turned out, two infantry battalion carrier platoons were also formed from personnel of HQ Sqn (Carrier Companies were to infantry divisions, tropical scale, what Divisional Cavalry Regiments were to infantry divisions, normal scale).

Some of these units were sent to New Britain, New Guinea and Torres Strait.