Even though Ireland was technically ‘neutral’, the IRA HATED the British, so it ‘allied’ itself with the Germans during WWI. And since it was the British who created the debacle known as ‘Palestine’, I can see the IRA joining forces with the PLO, later on.
Maybe WW II. The IRA was a legal army that fought with the Brits in the first war. My grandfather was gassed by the Germans.