It's not something that is often too clearly acknowledged by either tribe in modern Ireland, but there were a lot of Irish boys from both sides in the British trenches in WW1. Most of the Irish Volunteer Force (a pro-nationalist militia established in 1913 in response to the setting up of the Ulster Volunteer Force in the North) went to fight for Britain in the belief that a grateful Britain would grant them devolved rule following a successful war. Many of them never came back; those who did came back to a very changed country in the wake of the 16 Rising. The UVF in the north were, in an attempt to contain them as they were by the time the war broke out well armed and ready to make good on their promise to fight the British Army in order to resist Dublin rule and remain under the direct rule of Britain (yes, you read that correctly ), subsumed into the 36th Ulster Division, where they formed the broad majority of the troops (but by no means was it exclusively made up of UVF men; many others, not affiliated with the UVF and even a number of Northern Catholics joined up too). The 36th Ulster was one of the first sent over the top at the Somme (the more I read about some of those WW1 generals, the more I suspect this may be no coincidence given the feared threat of unrest they supposedly posed back at home), and suffered heavy losses on the first day. Many of these Irish boys, from wherever they came, would have seen a number of these images, as the British recruitment folks throughout the war produced many propaganda posters specifically aimed at the Irish market:
This first one refers specifically to the sinking of the Lusitania, an event mired in controversy:
This one is interesting in that it plays on the contemporary sense of "manliness" and "manly duty":
And another in the same vein:
Another aimed squarely at a large section of the Irish population bore the slogan:
"Fight for Ireland! Remember little Catholic Belgium!"
While "I'll go too! The real Irish Spirit!" was, if memory serves, squarely aimed at the men of the IVF in particular. Alas I can't find a digital image of either of those.