From the days when Horatius kept the bridge, down through the centuries to the World War, all leaders in battle were pictured at the front and with flaming sword, mounted on magnificent chargers, or otherwise so prominently dressed that all the world knew they were the leaders. During all these hundreds of years commands on the field of battle were by the voice, by the bugle, or by short range signals with arms, flags, and swords. Even where quite large forces were involved they were massed close enough ordinarily so that signalling by such means sufficed to cover the front of battle. In those cases where they did not, reliance was put upon swift couriers on horseback or on foot. With the invention of smokeless powder and the rifled gun battles were begun and carried on at greater and greater ranges. Artillery fired not only 2,000 to 3,000 yards but up to 5,000 and 10,000 yards, or even, as in the World War, at 20,000 yards and more. It was then that other means of signalling became essential. Distant signalling with flags is known to have been practiced to a certain extent on land for a long time. The extension of the telegraph and telephone through insulated wires laid by the Signal Service was the next great step in advance, and in the World War there came in addition the wireless telephone both on land and in aeroplanes and balloons. Along with this development, as mentioned under Screening Smokes, came the development of the use of smoke for protection and for cutting off the view of observers, thus making observation more and more difficult. This use of smoke, coupled with the deadly fire of machine guns and high explosives, forced men to take shelter in deep shell holes, in deep trenches and other places that were safe, but which made it nearly impossible to see signals along the front of battle. Every man can readily be taught to read a few signals when clearly indicated by definite, sharply defined colored smokes. At first these were designed for use on the ground and will be used to a certain extent in the future for that purpose, particularly when it is desired to attract the attention of observers in aeroplanes or balloons. In such cases a considerable volume of smoke is desired. For the man in the trench or shell hole some means of getting the signal above the dust and smoke of the battlefield is needed. It is there that signal smokes carried by small parachutes, contained in rockets or bombs, have proven their worth. These signals floating high above the battlefield for a minute or more, giving off brilliantly colored smokes, afford a means of sending signals to soldiers in the dust and smoke of battle not afforded by any other method so far invented. As before stated, every man can be taught these simple signals, where but very few men can be taught to handle even the simplest of wireless telephones.