You might have seen army truck drivers in cold places heating engines before starting the truckWhy do they do so?

You might have seen army truck drivers in cold places heating engines before starting the truckWhy do they do so?
Army truck driver heatthe engines because:1 the engines in army trucks are diesel which requires a hotter engine for starting and running. 2 in some places, like Alaska ,it gets down to -60F, even civilian cars have a hard time starting. 3: the engine might have frozen and needs to be thawed expediently and with no place to stow it indoors.