During winter fighting by the US army along the Imjun River during the Korean War, the engines of stationary trucks had to be kept running for 45 minutes in every hour to keep the engine oil from freezing.
Luftwaffe personnel in winter in Norway during WWII had to apply blowtorches to the engine sumps of Stuka bombers each morning to thaw the frozen engine oil .
I spent 3 winters in Norway with the royal Marines doing Arctic warfare training and we never ran engines unless we were going out in the vehicles and never had any problems with oil freezing.
The only precautions we took was to add a small amount of methonol to the diesel vehicles to make the engines start easier.
It's improved vastly, Toureman. It was the case then that you had to change the oil in your car between summer and winter. If temperatures became extreme, you might have had to to change it again. No multigrade oil in those days!
In Canada most cars are fitted with oil sump heaters to prevent the oil becoming too thick to do its job during the winter. When I was over there I saw many cars with a two pin mains plug hanging out of the radiator grille. When I asked what this was for I was told about the sump heater fitted to the cars. Some public car parks provide a mains outlet for you to plug into if leaving your car there overnight. This was done as well as changing the oil in October / November for a low viscosity ( thinner and runnier ) oil.
When I was in canada I too saw the plugs hanging out and was told it was to keep the temp up in the cooling system to stop it freezing, I would have thought this was more a priority than the oil.....