Simulators have been in use since the late-20's.
Link's first military sales came as a result of the Air Mail scandal, when the Army Air Corps took over carriage of U.S. Air Mail. Twelve pilots were killed in a 78-day period due to their unfamiliarity with Instrument Flying Conditions.
They have been invaluable in teaching instrument flying and emergency procedures ever since.
If you are hinting at pilots training on airliners, then the norm back then was for an airline to dedicate an airliner primarily for training. Flying good ol'circuits, touch and goes, and what not. Deals were made with airports with low traffic to accommodate those flights.
That was the case even for the Concorde, once the sim training was over, the pilots trained on the real thing. Nowadays pilots that have flown only small piston planes (for example), jump from Level D sims straight to revenue flights on jetliners.
(Source) The 'Blue Box' trainer from the early 1930s.