I heard this story, first hand, from someone who had been an observer on Sunderland flying boats in Northern Ireland, during WW2.
They were based on Lough Earne and, as has been mentioned in other threads, the aircraft were permitted to fly due West from there, crossing about 5 nm of the Republic, rather than have to fly NE for some 50 nm before turning W to avoid it. This was known, in some parts, as the 'Secret Air Corridor,' and saved about 150 nm each way to/from their Atlantic patrols.
My colleague said that, being fed up with rationing in NI, his crew decided to nip over the border, find an Irish pub, and have a few glasses of whisky (or should that be whiskey). So, one evening, they borrowed a 3 ton truck, all piled aboard and drove across the (completely unmanned) border. They drove to the west coast, and headed south, stopping at the first pub they saw.
They climbed out of the truck, all in uniform of course, went into the bar and ordered a round of drinks. As they waited, they looked behind the bar, through into the 'snug' and there, also in uniform, was a German U Boat crew! Both sides raised their glasses to each other, drank up and his crew then turned tail to rerurn, somewhat shocked, back to NI.
The view from their limited persepective at the time was that Ireland was allowing German vessels to berth.