Initially it served in East Anglia on anti-invasion duties, before being dismounted in 1915 and sent to take part in the Gallipoli Campaign.

It took part in the Sinai and Palestine Campaign in 1917 and 1918, before being transferred to the Western Front where it remained until the end of the war.

The Welsh Horse Yeomanry was raised on 18 August 1914[1] in South Wales by the Glamorganshire Territorial Force Association, with HQ at Sophia Gardens in Cardiff (since demolished).

[6] From early 1915, the 1st Line regiment was in 1/1st North Midland Mounted Brigade of 1st Mounted Division in the Diss area,[3] replacing the Leicestershire Yeomanry which had been posted to 7th Cavalry Brigade with the British Expeditionary Force on the Western Front.

It served as part of the Suez Canal Defences from 14 March to 26 July attached to 42nd (East Lancashire) Division;[11] it then joined the Western Frontier Force.

In March 1918, the battalion participated in the Battle of Tel 'Asur, but shortly afterwards was warned that it was to move to France, where reinforcements were urgently required to stem the German spring offensive.

[1] In July 1915 it was in the 2/1st South Wales Mounted Brigade as a fourth regiment in the Doncaster area.

The regiment was disbanded in early 1917 with personnel transferring to the 2/1st Montgomeryshire Yeomanry or to the 4th (Reserve) Battalion of the Royal Welsh Fusiliers at Oswestry.

[1][3] 25th (Montgomeryshire & Welsh Horse Yeomanry) Battalion, Royal Welch Fusiliers was reduced to cadre in France, and disbanded on 29 June 1919.

[14][5] None of the three regiments of the Welsh Horse Yeomanry was reformed in the postwar Territorial Force.