I recently picked my copy of Robert Fisk's "In Time of War: Ireland, Ulster and the price of neutrality". I first read the book for my Leaving Certificate, when my specialist subject was Operation Green and the W plan - the plans for the Germans and the British respectively to move their troops into what was then the Irish Free State. Although Green was very distinctly an invasion plan, the W plan was more ambiguous - officially it was a plan to move troops into the Free State to repel a German invasion, though certain aspects of the details and instructions given to British troops suggested that the British might not necessarily have been expecting the full cooperation of the Irish Defence Forces.
The Times is currently carrying a debate in their letters column about the Irish decision to remain neutral, which is a bit of a coincidence. It's even more of a coincidence that it comes on the same day that Neville Chamberlain has come bottom of a list ranking 20th century Prime Minsters in order of "greatness", in that it was Chamberlain's decision to return the Treaty ports that both enabled de Valera to keep Ireland out of the war at the same time as infuriating Churchill (at school, it was suggested that de Valera at the end of the Economic War had simply asked for them towards the end of the negotiations and was slightly surprised to get immediate agreement from the British).