Here’s an old timetable dated June 1, 1936 when the DC aircraft started in service and offered sleeper service. Technically lie flat, but more like Pullman bunks than lie flat seats.
And here’s a May 1,1948 depicting an American Overseas Airlines Lockheed L-049 Constellation used in transatlantic service. The technical stop required in Shannon had people getting off the aircraft while it was serviced (100-130 octane aviation gasoline, not nice calm Jet A, you wanted to get off). “All these wealthy people traveling through Shannon,” thought caterer Brendan O'Regan. And Ireland was financially poor but had Whiskey, beautiful lace, Belleek chinaware, Irish woolens, Waterford crystal and more.
Until that time cruise ship passengers were the ones who benefitted from duty free shopping.What are airplanes, he argued, but ships of the air? And what are airline passengers but sailors of the clouds? Why should they pay tax? In 1947, the Irish government agreed and let him try it out here. The rest is history...
(By that time I had flown in an AA DC-3 MEX-MTY-SAT.)
Link to more AA timetables from the World Airline Historical Society.