But in spite of all these and other discomforts, in spite of the disgusting vermin that crawled upon the men both in winter and in summer, both sides mastered the trenches and in the end learned to live in them with some degree of comfort. [Illustration: FORTS, FLYING AND NAVAL BASES ON THE NORTH SEA] At first the trenches were comparatively straight, shallow affairs; then as the artillery searched them out, as the machine gunners learned the art of looping their fire so that the bullets would drop into the hiding places of the enemy, the trench systems gradually became more scientifically involved. After the Germans had been beaten at the Marne and had retired to their prepared positions along the Aisne, there commenced a series of flanking attempts by one side and the other which speedily resolved itself into the famous “race to the sea.” This was a competition between the opposing armies in rapid trench digging. The effort on either side was made to prevent the enemy from executing a flank movement. In an amazingly short time the opposing trenches extended from the Belgian coast to the Swiss border, making further outflanking attempts impossible of achievement. This was not the first time in history that intrenched armies opposed each other. The Civil War in this country set the fashion in that respect. The contending sides in the Great War, however, improved vastly upon the American example. Communicating trenches were constructed, leading back to the company kitchens, and finally to the open road leading back to the rest billets of the armies. When night raiding commenced, it was speedily seen that straight trenches exposed whole companies of men to enfilading fire. Thereupon bastions were made and new defenses presented by zig-zagging the front-line trenches and the communicating ditches as well. To the formidable obstacles presented by the trenches, equipped as they were with sandbag parapets and firing steps, were added barbed-wire entanglements and pitfalls of various sorts. The greatest improvement was made by the Germans, and they added “pill boxes.” These were really miniature fortresses of concrete and armor plate with a dome-shaped roof and loopholes for machine gunners. Only a direct hit by a projectile from a big gun served to demolish a “pill box.” The Allies learned after many costly experiments that the best method to overcome these obstacles was to pass over and beyond them, leaving them isolated in Allied territory, where they were captured at the leisure of the attackers. Trench warfare brings with it new instruments. There are the flame projectors, which throw fire to a distance of approximately a hundred feet. The Germans were the first to use these, but they were excelled in this respect by the inventive genius of the nations opposing them.