It’s an interesting question, but mechanical rotor encryption machines fell out of favour reasonably quickly after WW2 (early 1960s?) - which suggests that even

It’s an interesting question, but mechanical rotor encryption machines fell out of favour reasonably quickly after WW2 (early 1960s?) - which suggests that even with the limited computing resources of the time they were no longer secure ie you don’t need brute force to crack messages, some other cryptanalysis technique could do it. Edit: Though it might have been that purely electronic cryptographic machines were just cheaper and stronger by that point.