So far as the ordinary petrol van or lorry is concerned, various types have been developed to meet a variety of commercial needs. A certain number of light vans are run on pneumatic tyres, but the solid tyre is preferred wherever economy is more important than speed. It of course goes without saying that, if a chassis is to run on solid tyres, it must be of substantial construction, and so designed that its mechanism will not be injured by the fact that the solid tyre is not so capable as the pneumatic of absorbing small vibrations. A very popular type of motor van is designed to carry about 25 or 30 cwt. These machines are capable of speeds up to about 25 or even 30 miles per hour in emergency, and can average comfortably 14 to 16 miles. Under reasonable conditions, they can cover daily journeys of 100 to 120 miles. Among larger types the 3-tonner predominates. This class of machine can be generally used for daily journeys of 70 to 90 miles, averaging perhaps 11 or 12 miles per hour. It usually consumes petrol at the rate of about 1 gallon to 8 miles, though better results are obtainable under good conditions. There are also a large number of 5-ton petrol lorries in commercial service. These can be advantageously used to cover 60 or 70 miles a day, consuming about 1 gallon of petrol to every 6 miles run. The motor cab runs about 20 to 25 miles on a gallon of petrol, and the motor omnibus about 7 to 10 miles. This question of fuel consumption is, of course, distinctly important in military service, when adequate supplies are only maintained at the right points with considerable difficulty. In later chapters some account is given of the attempts made by various governments to influence the development of motor traction into the directions dictated by their military needs, but this brief sketch of the general trend of events will be sufficient to indicate the present position, and to provide the necessary knowledge for the appreciation of the facts and considerations to which we shall now turn. CHAPTER II THE IMPORTANCE OF THE MILITARY MOTOR The Opinions of German and British Military Experts--The Old and New Methods of Transport and Supply--How Troops in the Field are Fed.