SAND, mud, and snow can present obstacles to military vehicles which are almost as tough to negotiate as manmade traps. With proper vehicle design these former obstacles can be made to become insignificant.
Cross-country operation is affected by two vehicle characteristics, flotation and traction. What is adequate flotation on one terrain is inadequate on another, and this same statement can be applied to traction. With track-laying vehicles, these factors are rather absolute, but with wheeled vehicles, inflation and tire stiffness may be important.
One other important thing affecting wheeled vehicles is the number of wheels which are driving. Wherever the coefficient of traction is low it is imperative that every wheel contacting the ground be able to contribute its share of forward tractive effort.
All these things add up to say that the only connection between the engine and the forward movement of a vehicle is the tires or tracks on which that vehicle rests, and it is for this reason that the principles of flotation and traction must be adhered to or cross-country operation may be impossible.