Aimed mainly at German armour, but apparently applicable to other Axis vehicles if you had the right key. http://www.oldmagazinearticles.com/pdf/German_ignition-system_1940.pdf
The keys were generally the same, BMW motorcycles used a similar key in the 60’s, maybe still do. The key only enables the lights, and ignition, but the fork lock had a regular pin/tumbler lock of the normal variety to prevent theft.
the key looked like a microphone jack, push it in, and the power comes on, turn it to one side, and the ignition is on.