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.