My dad had a 1939 Chevrolet and a defroster was an option. There was a box under the dash that contained a small radiator and fan, but there was no ductwork leading up to the slots under the windshield. Many motorists back then bought an accessory fan that clamped to the steering column and was aimed at the windshield. The first school bus I rode, a Wayne body on s 1939 GMC chassis had a fan mounted so it blew air on the windshield. That was the defroster.
Iām not quite sure why Iām responding to this necro-thread, but I want to point-out that many Subaru models have defrosting wires built into the base of the windshield, underneath where the wipers park. This feature can be very helpful when driving in winter weather.
My 14 highlander has a windshield wiper de-icer. Never used it yet. My car is garaged most of the time.