Seventeen Cavalry Reserve Regiments were formed by the British Army on the outbreak of the Great War in August 1914.
Although nominally cavalry, many of the drafts ended up being converted into infantry in order to satisfy the manpower demands of trench warfare.
Despite being training and not combat formations, several were involved in the putting down of the Easter Rising in Dublin in April 1916.
A little after noon on Easter Monday, a mixed troop of 9th and 12th Lancers, attached to the 6th Cavalry Reserve Regiment at Marlborough Barracks in Phoenix Park, was dispatched to investigate a "disturbance" at Dublin Castle.
[3] As they cantered down Sackville Street, they were fired upon by rebels who had taken up positions in and on the roof of the General Post Office.