At the outbreak of war, the Regiment was based in Belfast, but it was soon to be split up. 'A' Squadron moved to France during August 1914 and was attached to GHQ. In January 1916, it was transferred to 55th (West Lancashire) Division and, in May, formed the 1st North Irish Horse along with 'D' and 'E' Squadrons. In March 1918, the unit became a Cyclist Battalion.
'B' Squadron was attached to 59th (2nd North Midland) Division in August 1915, leaving in June 1916 to form the 2nd North Irish Horse with 'C' Squadron and the Service Squadron of 6th Inniskilling Dragoons. This unit was attached to X Corps until August 1917, when it was broken up and its personnel then transferred to infantry training with more than 300 of them joining 9th Bttn, Royal Irish Fusiliers.
'C' Squadron moved to France during August 1914 and was attached to GHQ. During April 1915, it was transferred to 3rd Division and, in June 1916, joined 'B' Squadron to form the 2nd North Irish Horse.
'D' Squadron was attached to 51st (Highland) Division in early 1915 and, in June 1916, joined 'A' and 'E' Squadrons to form the 1st North Irish Horse.
'E' Squadron was attached to 34th Division from early 1915 and, in June 1916, joined with 'A' and 'D' Squadrons to form the 1st North Irish Horse.
'F' Squadron was attached to 33rd Division from early 1915 until April 1916. It was then briefly attached in turn to 1st Cavalry Division, 49th (West Riding) Division and 32nd Division before being redesignated as 'B' Squadron during May 1916.
The Victoria Cross was awarded to one man from the North Irish Horse:
1914 - 4.
1915 - 4.
1916 - 4.
1917 - 10.
1918, up to 11th Nov - 26.
After 11th Nov 1918 - 0.
Note: A number of other North Irish Horsemen were killed while serving with the 9th Bttn (North Irish Horse) Royal Irish Fusiliers and other Irish and non Irish Regiments.