~12,000 citizens of the Irish Republic served in the
ASB that the Irish Free State weren't snivelling cowards who were blinded by Anglophobia
I mean. Yeah Battle of Atlantic is a bit easier.
Roughly 12,000 citizens of the Irish Republic served in the British armed forces (Army, RN, RAF) during WW II, and tens of thousands more were in the British and Irish merchant navies, British civil defense organizations, and British industry. In addition, Irish neutrality was decidedly partial to the Alllies, in terms of allowing British and American personnel who were interned to "escape," trade, intelligence, and joint planning in the event of Irish entry into the war - certainly far more so than any of the other European neutrals with the exception of Portugal (which allowed Allied use of Portuguese territory for base rights).
Ireland was a small, very weak and poor republic that had gained its independence from the UK less than two decades earlier, after a long and bloody struggle.
With all due respect, given all of the above, that's a more respectable record of contribution to the Allied cause in 1939-45 than (for example) Portugal (WW I member of the Allies), Switzerland (which after 1944, had an open border with France and, by extension, the Allies), and Sweden (which given the geographic circumstances, really could not have done more than it did until 1945).
In terms of the "white" dominions, the above is roughly equivalent to Newfoundland, which was even smaller and poorer (300,000 people compared to 3 million, more or less) but again, Ireland was independent; Newfoundland was a dominion.
In terms of the smaller independent allies, Ireland's population was significantly less than that of Cuba, which never sent any troops overseas (although the Cuban Navy participated in the naval war in the Caribbean and Gulf of Mexico, and is credited with the very respectable tally of multiple convoys escorted and one German submarine sunk).
So, all in all, Ireland's neutrality was certainly skewed in favor of the Allies; if Ireland had entered the war (after US entry presumably to provide some domestic political cover) and the Irish citizens serving in the British forces were allowed to transfer to the Irish forces, and overseas service was limited to volunteer (conscription for home service and coastal convoys), one could see (presumably) at least the historical 12,000 being sustained...
So cut that in half for replacements, and call it 6,000; figure one or two IrAF squadrons, and an infantry brigade group/regimental combat team ...
One could expect attachment to the US forces in NW Europe might go down a little easier than attachment to the British forces, so call it a fighter squadron (P-40 Warhawks transitioning to P-47 Thunderbolts?), a patrol/observation squadron (PBO Hudsons transitoning to PV-1 Venturas?), and an RCT. A USN patwing sets up shop in Ireland, itself, and the infantry RCT and fighter squadron go to France with the 12th Army Group.
Best,