Military signals to-day include the telephone, the telegraph, radio telegraphy and telephony, the buzzer, the buzzerphone, panels, pyrotechnics, flags, smoke signals, pigeons, dogs, mounted orderlies, and runners. Each of these means of signaling is an adjunct to the others; when one fails, another is employed to get the message through. Some have special uses for branches of the service with peculiar requirements. The radiophone is especially suited for communicating from airplanes. Artillery fire is directed by wire and wireless communication. Trained pigeons are sometimes able to get messages through when all other means of communication have failed.
The Army did not have a great quantity of signaling equipment when it went to war with Germany, but what it did have was good. The American punitive expedition in Mexico, where long lines of communication over rugged country were required, had given opportunity for testing modern signal apparatus in the field. Many of the signaling devices used by the American Expeditionary Forces were, at least in type, in common use by the civilian population; yet the procurement of this equipment offered heavy difficulties. This was because the Army was much more exacting than was commercial demand as to the quality of material used. For instance, a telephone instrument for use in the field hardly can be compared with the telephone in a business man's private office. The field set demands stronger connections, better insulation against the dampness of outdoor work, and more rugged construction to withstand rough usage by an army on the march.
One of the larger tasks of the Signal Corps in France was that of providing facilities for communication for the service of supply. The first Signal Corps officers sent to France soon realized that the forthcoming American Army could not depend upon the French telegraph and telephone systems in the various zones of operation, because those systems were already overburdened by the uses of the French government. Consequently, it became necessary to set up our own telegraph and telephone systems, extending them from the ports of debarkation through the various bases and zones up to the battle regions. The magnitude of the system which finally was constructed is shown in the fact that on November 11, the date of the armistice, there were in France 96,000 miles of American telegraph and long-distance telephone circuits. This wire was all used by the service of supply and by the various Army bases behind the front.
Yet in the field of fighting the requirements for wire were even greater. At one time during the height of the operations it was evident that the time was not far distant when the Signal Corps would need 68,000 miles a month of what was known as outpost wire, for use simply in connecting up the telephone and telegraph systems carried along by the troops in their advances.
Outpost wire was entirely a development of the war against Germany. The original telephone system used at the front had been the single telephone wire grounded to complete the circuit. But all the armies in France perfected their listening instruments to such a degree that they could hear conversations conducted on the grounded telephone circuits, the sounds being detected in the earth itself. Consequently, it became necessary to carry forward with troops two-wire telephone circuits, thus doing away with ground connections. Even then care had to be taken that the insulation of this double wire was perfected, lest the impulses enter the ground through gaps in the insulation. Wireless for outpost communication was equally impracticable, since the enemy could easily listen in and hear radio phone messages.
Outpost wire insured secret communication at the front. Outpost wire was a twist of two wires, each single wire being made up of seven fine wires, four of them of bronze, and three of them of hard carbon steel. These were stranded together, coated, first with rubber and then with cotton yarn, and finally paraffined. The wire was produced in six colors—red, yellow, green, brown, black, and gray—for easy identification in the field, each unit employing its own color.
The wastage of outpost wire was enormous. In an advancing movement it was folly to undertake to pick up the wire. The abandoned miles of it had to be left in the field to be salvaged later by the clean-up parties.
The proposition of producing 68,000 miles of outpost wire every month staggered the wire manufacturers of the country. There were not enough braiding machines to complete such an order, and new ones had to be built before such a quantity of outpost wire could be attained.
In addition to the various means of communication, the Signal Corps was also called upon to supply in large quantities such other articles as wire reel carts, flag staffs, field glasses, photographic equipment, chests, tools, meteorological apparatus, and wrist watches.