When Germany embarked upon its policy of frightfulness, it held in reserve murderous inventions that had been contributed to the German General Staff by chemists and other scientists working in conjunction with the war. Never since the dawn of time had there been such a perversion of knowledge to criminal purposes; never had science contributed such a deadly toll to the fanatic and criminal intentions of a war-crazed class. As the war uncoiled its weary length, and month after month of embargo and privation saw the morale of the German nation growing steadily lower, these murderous inventions were successively called into play against the Allies, but as each horror was put into play on the battle-field, its principles were solved by the scientists of the Allied nations, and the deadly engine of destruction was turned with trebled force against the Huns. This happened with the various varieties of poison gas, with liquid fire, with trench knives, with nail-studded clubs, with armor used by shock troops, with airplane bombs, with cannon throwing projectiles weighing thousands of pounds great distances behind the battle lines. Not only did America and the Allies improve upon Germany's pattern in these respects, but they added a few inventions that went far toward turning the scale against Germany. An example of these is the "tank." Originally this was a caterpillar tractor invented in America and adopted in England. At first these were of two varieties, the male, carrying heavy guns only, and the females, equipped with machine guns. To these was later added the whippet tank, named after the racing dog developed in England. These whippet tanks averaged eighteen miles an hour, carrying death and terror into the ranks of the enemy. All the tanks were heavily armored and had as their motto the significant words "Treat 'Em Rough." The Germans designed a heavy anti-tank rifle about three feet longer than the ordinary rifle and carrying a charge calculated to pierce tank armor. These were issued to the German first line trenches at the rate of three to a company. That they were not particularly effective was proved by the ease with which the tanks of all varieties tore through the barbed wire entanglements and passed over the Hindenburg and Kriemhild lines, supposed by the Germans to be impregnable. The tanks in effect were mobile artillery and were used as such by all the Allied troops. Germany frantically endeavored to manufacture tanks to meet the Allied monsters, but their efforts were feeble when compared with the great output opposed to them. Before considering other inventions used for the first time in this war, it is well to understand the tremendous changes in methods and tactics made necessary by these discoveries.