Royal Irish Regiment
18th Regiment of Foot
National Army Museum
1st Bn. Regular. 04 Aug 1914 at Nasirabad in the Nasirabad Brigade, 5th (Indian) Division.
2nd Bn. Regular. 04 Aug 1914 at Devonport in the 8th Brigade, 3rd Division.
3rd (Reserve) Bn. Regular. Stayed in the UK and supplied drafts to the Regular Battalions overseas.
4th (Extra Reserve) Bn. Regular. Stayed in the UK and supplied drafts to the Regular Battalions overseas.
5th (Service) Bn. K1. Formed at Clonmel on 29 Aug 1914 in the 29th Brigade, 10th Division.
6th (Service) Bn. K2. Formed at Clonmel on 06 Sep 1914 in the 47th Brigade, 16th Division.
7th (South Irish Horse) Bn. Territorial Force. Formed in France from the 1st and 2nd Bns South Irish Horse on 01 Sep 1917. Joined the 49th Brigade, 16th Division on 14 Oct 1917.
8th (Service) Bn. Formed in France from the 2nd Garrison Guard Bn on 25 May 1918 in the 178th Brigade, 59th Division.
1st Garrison Bn. Formed at Dublin on 02 Aug 1915. Went to Gallipoli.
2nd (Home Service) Garrison Bn. Formed at Dublin in Mar 1916. Stayed in the UK until Apr 1918 when it went to France (renamed 2nd Garrison Bn) joining the 178th Brigade, 59th Division.
The Regular Reserve Battalions may also have supplied drafts to the Service Battalions as well as the Regular Battalions.