Car ownership and driver education is commonplace nowadays, but during WW1 especially, motor vehicles were a novelty and few people owned or could drive them in civilian life. How did they find or train people to know how to drive even a Model T, let alone bigger trucks?
Maybe farmers used to driving tractors were sought out?
Were mechanical tractors common then either? I remember an account of how farmers in that era still used draft animals to pull plows and wagons.
On the bigger, wealthier farms you would find some equipment but obviously not in the numbers a war would require. I imagine they’d have more luck in cities with a lot of manufacturing as many of them began adopting vehicles to move goods faster than by wagon. Still, not a lot to pull from regardless.
Bus drivers, taxi drivers.
Buses were used to get British troops to the front and French taxis did the same for the French so there were people driving. Drivers were trained to drive the tanks and the automobile had been around for a while by then.
London during WWI
Same way you train some 18 year old to drive a tank today. Through the 1910s version of Death by PowerPoint and the sheer brute force and willpower of some exasperated NCO.
Once militaries decided to incorporate motor vehicles into their ranks, they recruited people with the necessary skills to operate and maintain them and then developed a training curriculum. In the case of the US for example they may very well have had “experts” from Ford give the initial instruction.
From then on, it’s a simple matter of propagation and practice. And the more people you train, the more you now theoretically have available to train others.
This picture reminds me of a television special I saw as a child, where drivers were trained to drive double-decker busses for London. The last step in the final exam had to have the drivers know how to swerve properly on a wet and very slippery road.
I’m guessing they used the same method my Dad described when he was drafted in 1945 - ten minutes of instruction from an NCO on the controls of a CCKW followed by three laps of the motor pool! Anyone who managed without destroying the surrounding buildings or his own truck was handed a license - there was still a war on…