This has been called an engineers’ war; it is certainly the first war in which petrol-propelled mechanical transport has been employed to any extent. Thousands of Army Service Corps motor-lorries, painted service grey-green, line the roads behind the trenches in France and Flanders. Petrol is surely the key to modern warfare. Operations on such a gigantic scale could not be carried on without it, for petrol-propelled vehicles are used, amongst other purposes, for the following:— The conveying of food, clothes, ammunition, and water to the troops. The haulage of heavy pieces of artillery. The evacuation of sick and wounded to the casualty clearing hospitals, etc. The rapid movement of troops from one part of the line to another, and as the quickest means of bringing up reinforcements. The fate of Paris was largely changed, at the beginning of the War, by the requisition and mobilization of some thousand or so motor taxi-cabs during a night, at the order of the late General Galliéni. In them were sent out twenty-five thousand troops, who by this means of transport swiftly proceeded to the Ourcq and reinforced the French Army, which was striking a terrific blow at the turned flank of Von Kluck’s army. It will be recalled that the enemy’s columns advancing on Paris turned abruptly eastwards to unexpectedly rush on the British Divisions and cut them off from their juncture with the 5th French Army. They failed to do so, but until the night of September 9th-10th the battle of Nanteuil-sur-Marne hung in the balance. General Maunoury’s army was constantly being reinforced, however, by the troops which arrived at Dammartin and other points in the requisitioned taxi-cabs so regularly that the pressure was increased, the tide of battle turned, and the capital of France saved. The stand put up by the allied French and British Armies on the Marne will go down to posterity as the most epic battle in European history. The warfare in France and Flanders, since it settled down to a prolonged and continuous trench _strafe_, has been described as consisting in "months of boredom punctuated by moments of intense fear," and it has been to pass the time of day during some of those months that the following chapters have been written. If they succeed in giving the reader some slight idea of the scope, extent, and versatility of work accomplished by the mechanical transport of the Army Service Corps, of how our armies in the field are fed, and of the soldier-man’s life and surroundings at various distances "behind the front"—what he sees and does there—they will not have been written in vain. I have purposely avoided matters of controversy, and I have written not as a critic but as an observer and the player of a very small part in the great drama. I trust that the varying degrees of discomfort, inseparable from active service, under which I have had to write will be accepted as sufficient excuse for any lack of literary style.