How was Ireland involved in World War 2?
150,000 Irish people North and South volunteered to fight against Nazi tyranny in Europe, at least 10,000 of whom were killed while serving in British uniforms. Secretly: they provided Atlantic weather reports that especially helped in the D-day landings, repatriated stranded British servicemen, captured German spies, and allowed an air corridoor for anti submarine patrols beyond Donegal.
The Irish Free State (as it then was) kept out of the war. Northern Ireland fought as a part of the United Kingdom.