Another substitution that passes almost unnoticed today was elevator operators.

Elevators were complicated equipment which could kill people (and still occasionally do).

Otis's Safety Brake (1850) made elevators possible, but it was automated controls (and scheduling systems) which made self-service elevators possible. Apparently stimulated by an elevator operators strike in 1945:

<https://www.linkedin.com/pulse/historical-event-pushed-eleva...>

Fully-automated self-service elevators still took about a decade to appear, but would have been fairly common by the late 1950s / 1960s.