Turning to the second factor, that of vulnerability _in battle_, here again a new weapon has revolutionized the methods of warfare by providing soldiers with a machine-made skin to offset the deadliness of modern fire. Not that armour is a new invention, but until the advent of the tank provided him with mechanical legs, man’s muscle-power was insufficient to move him when enclosed in an armoured shell. Navies changed long ago from muscle-power to machine-power, alike for hitting, protection, and movement. Armies had to lag behind until the invention of the motor because they could not ask the already over-burdened foot-soldier to carry armour――if he had been given it he could not have moved it. Now, however, that a means has been invented, is it not irrational to stand out against the lessons of national progress, to refuse to free the soldier’s mind and spirit――his real military assets――from the fetters imposed by his bodily limitations? Military conservatives are prone to talk of “Men _v._ Machines,” as if they were conflicting ideals, whereas in reality neither opposition nor comparison is possible. We should not fall into the absurdity of comparing man with a locomotive or a sculptor with his tools, and mechanical weapons are but the instruments of man’s brain and spirit. The reactionary who opposes the inevitable course of evolution forgets that the question of muscle-force _versus_ machine-force was settled away back in the Stone Age when the prehistoric fighting man discovered that a flint-axe was a more potent weapon than his bare fist. Moral depends ultimately on confidence, and even the finest troops will lose their moral if they are reduced to the _rôle_ of mere human stop-butts, powerless to hit back. The layman is apt to feel mystified by the fog of technical controversy that surrounds the merits of the various arms. To dissipate this by a breeze of common sense, let us put the simple question: How can the old-established arms combat the new――tanks and aircraft? First, infantry――whose weapons are machine-guns, light automatics and rifles. They cannot attack the tank, because even if they had weapons that could penetrate the tank’s armour, the latter’s speed would enable it to avoid conflict at will. Similarly, infantry have no power to hit the aeroplane unless it swoops very low, whereas it can remain at a moderate height and bomb its helpless foes. For defence against either, infantry are dependent on the help of other arms or on going to earth like rabbits――in which case their offensive value in war is _nil_. A business which retained the aged and infirm as the bulk of its employees would soon be bankrupt; it may find use for a few as caretakers――and that is the only feasible _rôle_ for infantry in mobile warfare of the future.