There is a phrase at the bottem of the battle flag flown during the American Civil War by the 69th New York Volunteers, that I cant find a translation for.
RIATDH DAR OHRUIO O SPARIO IANN
Any help would be greatly appreciated.

This link should help:

U.S. Civil War/Union Brigade Motto

Caoimhín

Interestingly there is an Irish battalion based in Galway that conducts it's training and activities through Gaeilge called An Chéad Cath.