RoI in WW2
While Ireland needed to maintain an appearance of neutrality during the War, in January 1941 the UK government negotiated the Donegal corridor via a secret treaty with the Irish Free State. This enabled the Catalinas and Sunderlands operating out of Castle Archdale to reach 100 miles or more further into the Atlantic compared to the previous route flying entirely over Northern Irish territory and crossing the coast near Derry.
While primarily aimed at improving convoy cover and reducing the mid-Atlantic gap that could not be reached by anti-submarine aircraft operating from either side of the Atlantic, the Donegal corridor also enabled the Catalina that spotted the Bismarck to have the required range.
There's an interesting small museum at Castle Archdale comemmorating the wartime flying boat operations.