How to both the Allies and the Germans the solution by artillery was the first to occur. How, secondly, we and the Germans each according to our national habits of mind, thought of another solution. The Germans--who were chemists--of gas, used treacherously in despite of signed undertakings to the contrary; we, who were mechanics, of a self-propelled shield, from behind which we could direct an effective fire. He knows how gas was countered, after the first surprise, by means of various air-filtering devices; but how the Tank gradually revolutionised warfare, because there was no particular specific or antidote to the Tank, which depended not so much upon surprise as on the simple factors of its enormous fire power, and its ability to surmount obstacles. For whether the troops attacked had fought against Tanks before or no, the Tank crushed down wire and smothered machine-gun fire just the same. Marshal Foch is the first of our witnesses. He sketches the evolution of the Tank, and describes the circumstances which called it into being, in his foreword to the English translation of his republished _Principles of War_. He has dealt with the old slowness of “digging in.” We translate his words literally: “The machine-gun and the barbed-wire entanglement have permitted defences to be organised with indisputable rapidity. These have endowed the trench, or natural obstacle, with a strength which has permitted offensive fronts to be extended over areas quite impracticable until this time.... The offensive for the time was powerless, new weapons were sought for, and, after a formidable artillery had been produced Tanks were invented--_i.e._ machine-guns or guns protected by armour, and rendered mobile by petrol, capable, over all types of ground, to master the enemy’s entanglements and his machine-guns.... “Thus it is the industrial power of nations that has alone permitted armies to attack, or the want of this power has reduced them to the defensive.” Monsieur Loucheur--in January 1919 French Minister of Munitions--was a strong advocate for Tanks in the French Army. “There are two kinds of infantry: men who have gone into action with Tanks, and men who have not; and the former never want to go into action without Tanks again.” Sir Douglas Haig’s summing up in his Despatch, though necessarily conservative, is not therefore the less significant: