I've heard that Johnny Brown, who wrote the Kilnamartyra Exile lyrics, had joined the British Army when he was young and that he survived the Battle of the Somme. When he returned from WW1 to Ireland, Brown never left Ireland again. He eventually became a John of God lay brother.

The author of Cath Céim an Fhia is Máire Bhui ni Laoghaire https://www.dib.ie/biography/ni-laoghaire-maire-bhui-a6189