In addition to their two Regular battalions, the Royal Irish Regiment raised a number of Service, and home based Reserve and Garrison battalions.
Total - 12:
Regular - 2. Service - 4. Reserve - 2. Garrison - 2.
At the outbreak of war, they were based at Nasiribad in India and joined 82nd Brigade, 27th Division in France during December 1914.
In November 1915, the battalion sailed with the Division for Salonika where a year later, in November 1916, they transferred to 30th Brigade, 10th (Irish) Division and with whom they served until the end of the war in Palestine.
At the outbreak of war, they were based in Devonport and, as part of 8th Brigade, 3rd Division, landed in France during August.
The battalion was virtually destroyed during the Battle of La Bassée and were subsequently transferred to Army reserve in October 1914.
In March 1915, they transferred to 12th Brigade, 4th Division and four months later onto 11th Brigade. In May 1916, they transferred to 22nd Brigade, 7th Division and eventually, in October 1916, to 49th Brigade, 16th (Irish) Division.
Finally in April 1918, they transferred to 188th Brigade, 63rd (Royal Naval) Division.
Formed in August 1914, they joined 29th Brigade, 10th (Irish) Division before converting to the Division's Pioneer Battalion during June 1915.
In July 1915, the battalion sailed with the Division to Gallipoli, landing at Suvla Bay in August.
They moved with the 10th (Irish) Division to Salonika in September 1915 and spent over two years with them until April 1918 when the battalion was transferred to 52nd (Lowland) Division.
They moved soon afterwards to France, where they transferred to 50th (Northumbrian) Division to become their Pioneer Battalion during July 1918.
Formed in September 1914, they joined 47th Brigade, 16th (Irish) Division.
They arrived in France with the Division in December 1915 and served with them until the battalion was disbanded in February 1918.
Formed in France during September 1917 from the dismounted 1st and 2nd South Irish Horse, they joined 49th Brigade, 16th (Irish) Division.
In April 1918, the battalion was reduced to cadre strength before being reformed in June and them immediately transferred to 21st Brigade, 30th Division.
Formed originally in Ireland during March 1916 as the 2nd Garrison Guard Bttn they eventually arrived in France during April 1918.
In June 1918, the battalion transferred to 121st Brigade, 40th Division before being renamed as 8th Bttn in July 1918.
The Victoria Cross was awarded to one man, who was serving with the Royal Irish Regiment during the First World War:
2,766 men from the Royal Irish Regiment are listed in the CWGC database of First World War deaths: