The most important of the supplies just mentioned, in a purely military point of view, is that of munitions. For side by side with other improvements has gone the evolution of artillery. Foreshadowed in the Balkan wars, it is accepted as a principle that an army must be accompanied not only and merely by the classic field piece of small calibre, but also by large-calibred pieces, effective not only against troops, but against positions as well, and not only against positions taken as the fortune of war may dictate, but against positions, i.e., fortresses, or their future substitutes, carefully prepared in time of peace. For the evolution of artillery has caused fortresses as such to lose their value : Liege, Namur, Maubeuge, Antwerp proved of no account, and if Verdun held out, it was not because of its strength as a fortress, but simply because it had become a sector in a long line, like that of Ypres or Arras. It has been made abundantly clear by the war that cities, capitals, fortresses and provinces will be taken in vain, so long as the enemy army remains unbeaten.
When two armies are besieging each the other, and resting on impassable flanks, only frontal attacks are possible: this has •produced a strength of trench that can be overcome only by the intensest long-continued artillery fire using high-explosive shell, an expense of am munition made possible only by mobilization of industries. Under these conditions, "lines" have become literally areas of trenches, one line behind the other, joined by communica tions. The capture of a first line may be a success of no value. In the defense of these entrenched lines, the machine-gun has played during the European War, and will play in the future, in field-, as well as in position fighting, a part of the first importance. Mining and counter-mining, heretofore used only in sieges of regular fortresses, will have peculiar weight when two entrenched armies face each other over a long front impossible to flank. And these armies will normally live, move and have their being under the ground.
A feature of trench warfare in the World War was the occasional hut deliberate use of asphyxiating gases and burning liquids.
Whether in the future this violation not only of The Convention but of fundamental humanity will be endured only experience can tell but there is every reason to believe that asphyxiating gases have come to stay. The end of the war saw them used in cloud form, and in projectiles (projection and artillery pro jectile proper). That ts, the gas projectile had won its right in open warfare, and had become as much a necessity as the shrapnel itself.
The greatest advance in the military art proper has resulted from the application of aeronautics, the great contribution of the 20th century. First shown to be practicable by the Wright brothers, aviation, neglected in America, was at once seriously taken up by the French and converted to military use. The rest of the world (the United States and Great Britain excepted) soon followed suit. The aeroplane has been without influence on strat egy, but has profoundly affected tactics. It has made surprise well-nigh impossible and dissi pated the fog of war. Thanks to its assistance a commanding general now sees the enemy, and what is more sees him almost at once. Hence combinations of troops, movements, con centrations are reported almost as soon as made, intentions laid bare and adequate meas ures of prevention made possible in good time. The aeroplane moreover has proved itself in dispensable to the artillery by correcting fire and by detecting hostile batteries whose emplace ments would otherwise be unknown. As an agent of destruction, it was not nearly so useful at first as it was in the acquisition of informa tion. But as the war progressed bombing be came generalized on both sides; with direct military results when employed against railway stations, depots, ammunition dumps, troops in concentration and even in combat. The airship (Zeppelin) has on the whole disappointed ex pectation : it should be recollected, however, in respect of both airships and aeroplanes that the whole subject, in spite of the experience of the Great War, is still visibly in its infancy. See