Stage by stage the difficulties were overcome. First it was the Germans who with their terrible Fokker planes harnessed the machine-gun to the airplane and made of it a weapon of offense. Then it was the Allies who added the radio and made of it an efficient method of observation and spotting of artillery fire. Increased engine-power began to be developed, and bombs were carried in ever-increasing numbers and size.

The moment an enemy plane fell on either side of the line the victors gathered about their prey with a keenness which could come only of the hope that they might find in it some suggestion that would make their own flying more efficient. Each learned from the other, so that the different schools on either side of the line had all the advantage of watching the development of their rivals. Very shortly after an improvement appeared on one side it reappeared in the planes of the other side.

It is doubtful if ever a more desperate scientific battle was fought than that which featured the development of the air services of the various belligerents during the war. Control of the air was so vital that neither could afford to overlook any possibility; and, as a result, the scientific evolution was truly astounding. No man was reserved on this subject of airplane improvement. All contributed their best skill and ability to the common reservoir of knowledge.

Very soon man's conquest of the air became so complete that different types of planes were developed for different kinds of work. The plane of the early days which wandered off by itself wherever it saw fit, gathered what information it could, and returned to drop a note to the commander below, developed into a highly efficient two-seated plane equipped with machine-guns for protection against attack, wireless for sending back messages, and cameras for photographing the enemy's positions below. The plane which had earlier dropped an occasional bomb in a hit-or-miss fashion over the side now developed either into a powerful two-seater with a great weight-carrying capacity and a continually more efficient scientific method of aiming its missiles or into a huge machine for long-distance night-bombing work capable of carrying from two to a dozen men and from two to four tons of bombs. During this time the strictly fighting plane, usually a single-seater, increased in speed, "ceiling," and agility till it could dart, twist, and dive about, three to five miles above the trenches, protecting friendly bombing and observation planes below from enemy attack or swooping down to send enemy planes in flames to the ground.

Vital though all this work was for the war, it had an incomparably greater value for the perpetual struggle which all mankind is waging against nature. While the various nations were seeking to destroy one another through the air, they were in reality destroying the chains which bound them to the ground and winning their freedom in a new element. The advance which the Allies or the Germans made over each other in scientific aerial development was a joint advance over the restrictions of gravitation.

This, indeed, apart from the spread of democracy and internationalism, may well stand out in history as the war's richest heritage. Problems which had been considered insoluble were solved. The casting aside of all conventions, all restrictive habits of thought, all selfishnesses, and the focusing of the highest scientific ability in a struggle which might mean the life or death of the nation, had brought as a by-product a development beyond our wildest fancies.

Aerial operations in any future war, however, will have at once a problem which has only recently and in very much smaller degree confronted the navy, namely, the assurance of attack not only on the front, in the rear, and on both flanks, but from above and below as well. Recently the navy has had to face that problem—submarines operating below and airplanes above; but the problem of attack upon a ship is not so serious as upon an airplane.

Already, in order to meet this danger of attack from every possible direction, a most complete strategy and system of formations have been worked out. In this way the various types of planes operate in different air strata according to their missions, the upper planes echelon somewhat behind those below on the order of a flight of steps facing the enemy. This system provides a quick method of reception of an attack and the assurance of quick support, no matter where the attack may come. Obviously there would be nothing in all of warfare on either land or sea comparable to a collision between two such aerial fleets. The speed of the lighter planes, quick, life-taking duels in several different strata at once, would provide a clash of action, speed, and skill far more beautiful and yet in many ways far more terrible than anything ever recorded in the history of war.

Fleets of the skies—who shall attempt at this day of the infancy of the science to limit their scope? Aerial battle-planes of colossal size and power are as certain to come in time, and in not a very long time, as the dreadnought of to-day was certain to follow the first armored ship of only a half-century ago. Never yet has man opened up a new avenue of war that he has not pursued it relentlessly to its final conclusion. It is certain that he will not fail to push aerial development with all the energy with which he has devoted himself to the science of destruction.

The avenue of the seas has been up to now the world's greatest civilizer. Very shortly, without doubt, it will be replaced by the avenue of the skies. If we are to strive for freedom of the seas, what shall we say about freedom of this new element? The laws of aerial travel and aerial warfare open an unlimited field of speculation.