But, in WW2 it was a different matter.
I had the privelege of chatting to a gentleman who was an observer on Sunderlands, based on Lough Erne, at the western end of Northern Ireland. They spent long hours on patrol, sub-hunting over the North Atlantic.
One night, his crew decided to nip over the (un-policed) border into the ROI, where there was no rationing. In uniform, they borrowed a truck, travelled the 5 miles to the ROI coast, and headed south to find the first pub.
They all piled into the bar and ordered a round of whiskies, As they were waiting to be served, they looked through the bar, and into the 'snug' and came face to face with a German U Boat crew!