The onset of World War I found the opposing armies equipped to a varying degree with modern means of signal communication but with little appreciation of the enormous load that signal systems must carry to maintain control of the huge forces that were set in motion. The organization and efficiency of the armies varied greatly. At one end of the scale was Great Britain, with a small but highly developed signal service; and at the other end stood Russia, with a signal service inferior to that of the Union Army at the close of the American Civil War. The fact that commanders could not control, coordinate, and direct huge modern armies without efficient signal communication quickly became apparent to both the Allies and the Central Powers. The Germans, despite years of concentration on the Schlieffen Plan, failed to provide adequately for communication between higher headquarters and the rapidly marching armies of the right wing driving through Belgium and northern France. This resulted in a lack of coordination between these armies, which caused a miscarriage of the plan, a forced halt in the German advance, and the subsequent withdrawal north of the Marne. On the Allied side, the debacle of the Russian forces in East Prussia--a crushing defeat at the hands of General Paul von Hindenburg in the Battle of Tannenberg --was largely due to an almost total lack of signal communication.
As the war progressed there was a growing appreciation of the need for improved electrical communications of much greater capacity for the larger units and of the need within regiments for electrical communications, which had heretofore been regarded as unessential and impractical. Field telephones and switchboards were soon developed, and those already in existence were improved. An intricate system of telephone lines involving thousands of miles of wire soon appeared on each side. Pole lines with many crossarms and circuits came into being in the rear of the opposing armies, and buried cables and wires were laid in the elaborate trench systems leading to the forwardmost outposts. The main arteries running from the rear to the forward trenches were crossed by lateral cable routes roughly parallel to the front.
Thus, there grew an immense gridwork of deep buried cables, particularly on the German side and in the British sectors of the Allied side, with underground junction boxes and test points every few hundred yards. The French used deep buried cable to some extent but generally preferred to string their telephone lines on wooden supports set against the walls of deep open trenches. Thus electrical communication in the form of the telephone and telegraph gradually extended to the smaller units until front-line platoons were frequently kept in touch with their company headquarters through these mediums.
Despite efforts to protect the wire lines, they were frequently cut at critical times as the result of the intense artillery fire. This led all the belligerents to develop and use radio (wireless) as an alternate means of communication. Prewar radio sets were too heavy and bulky to be taken into the trenches, and they also required large and highly visible aerials. Radio engineers of the belligerent nations soon developed smaller and more portable sets powered by storage batteries and using low, inconspicuous aerials. Although radio equipment came to be issued to the headquarters of all units, including battalions, the ease of enemy interception, the requirements for cryptographing or encoding messages, and the inherent unreliability of these early systems caused them to be regarded as strictly auxiliary to the wire system and reserved for emergency use when the wire lines were cut. Visual signaling returned to the battlefield in World War I with the use of electric signal lamps. Pyrotechnics, rockets, Very pistols, and flares had a wide use for transmitting prearranged signals. Messenger service came to be highly developed, and motorcycle, bicycle, and automobile messenger service was employed. Homing pigeons were used extensively as one-way messengers from front to rear and acquitted themselves extremely well. Dogs were also used as messengers and, in the German army, reached a high degree of efficiency.
A new element in warfare, the airplane, introduced in World War I, immediately posed a problem in communication. During most of the war, communication between ground and air was difficult and elementary. To make his reports the pilot had to land or drop messages, and he received instructions while in the air from strips of white and black cloth called "panels" laid out in an open field according to prearranged designs. Extensive efforts were made to use radiotelegraph and radiotelephone between the airplanes and ground headquarters. The closing stages of the war saw many planes equipped with radio, but the service was never satisfactory or reliable and had little influence on military operations.
During World War I, wireless telegraph communication was employed extensively by the navies of the world and had a major influence on the character of naval warfare. High-powered shore and ship stations made wireless communication over long distances possible.
One of the war lessons learned by most of the major nations was the compelling need for scientific research and development of equipment and techniques for military purposes. Although the amount of funds devoted to military development during the period from World War I to World War II was relatively small, the modest expenditures served to establish a bond between industry, science, and the armed forces of the major nations.
Of great importance in postwar radio communication was the pioneering by amateurs and by industry and science in the use of very high frequencies. These developments opened up to the armed services the possibilities of portable short-range equipment for mobile and portable tactical use by armies, navies, and air forces. Military work in these fields was carried out actively in Germany, Great Britain, and the United States. As early as 1938 Germany had completed the design and manufacture of a complete line of portable and mobile radio equipment for its army and air force.
Between World Wars I and II the printing telegraph, commonly known as the teleprinter or teletypewriter machine, came into civilian use and was incorporated in military wire-communication systems, but military networks were not extensive. Before World War II, military radioteleprinter circuits were nonexistent.
Another major communication advance that had its origin and early growth during the period between World Wars I and II was frequency-modulated (FM) radio. Developed during the late 1920s and early 1930s by Edwin H. Armstrong, an inventor and a major in the U.S. Army Signal Corps during World War I, this new method of modulation offered heretofore unattainable reduction of the effect of ignition and other noises encountered in radios used in vehicles. It was first adapted for military use by the U.S. Army, which, prior to World War II, had under development tank, vehicular, and man-pack frequency-modulated radio transmitters and receivers.
On the eve of World War II, all nations employed generally similar methods for military signaling. The messenger systems included foot, mounted, motorcycle, automobile, airplane, homing pigeon, and the messenger dog. Visual agencies included flags, lights, panels for signaling airplanes, and pyrotechnics. The electrical agencies embraced wire systems providing telephone and telegraph service, including the printing telegraph. Both radiotelephony and radiotelegraphy were in wide use, but radiotelephony had not as yet proved reliable and satisfactory for tactical military communication. The navies of the world entered World War II with highly developed radio communication systems, both telegraph and telephone, and with development under way of many electronic navigational aids. Blinker-light signaling was still used. The use of telephone systems and loud-speaking voice amplifiers on naval vessels had also come into common use. Air forces employed wire and radio communication to link up their bases and landing fields and had developed airborne long-range, medium-range, and short-range radio equipment for air-to-ground and air-to-air communication.
In communications electronics, World War II was in one sense similar to World War I: the most extravagant prewar estimates of military requirements soon proved to represent only a fraction of the actual demand. The need for all kinds of communication equipment and for improved quality and quantity of communications pyramided beyond the immediate capabilities of industry. An increase in manufacturing plant became vital, and research and development in the communications-electronics field was unprecedented. The early German blitzkrieg, with tank and armoured formations, placed a new order of importance on reliable radio communication.
The development of the air, infantry, artillery, and armoured team created new requirements for split-second communication by radio among all members. Portable radio sets were provided as far down in the military echelons as the platoon. In every tank there was at least one radio and in some command tanks as many as three. Multiconductor cables were provided wire communications; they could be reeled out rapidly and as many as four conversations could take place on them simultaneously through the use of carrier telephony. The Germans were the first to use this type of military long-range cable, and their example was followed promptly by both the British and the U.S. forces. High-powered mobile radio sets became common at division and regimental level. With these sets telegraph communication could be conducted at distances of more than 100 miles (160 kilometres) with vehicles in normal motion on the road. Major telephone switchboards of much greater capacity were needed. These were developed, manufactured, and issued for use at all tactical headquarters to satisfy the need for the greatly increased number of telephone channels required to coordinate the movements of field units whose mobility had been expanded many times.
Radio relay, born of the necessity for mobility, became the outstanding communication development of World War II. Sets employing frequency modulation and carrier techniques were developed and used, as were also radio relay sets that used radar pulse transmission and reception techniques and multiplex time-division methods for obtaining many voice channels from one radio carrier. Radio relay telephone and teletypewriter circuits spanned the English Channel for the Normandy landing and later furnished important communication service for General George S. Patton, after his breakout from the Normandy beachhead.
The need for communication between the homelands and many far-flung theatres of war gave rise to the need for improved long-range overseas communication systems. A system of radioteletypewriter relaying was devised, by which a radioteletypewriter operator in Washington, London, or other capitals could transmit directly by teleprinter to the commander in any theatre of war. In addition, a system of torn-tape relay centres was established so that tributaries could forward messages through the major centres and retransmit quickly by transferring a perforated tape message from the receiving to the transmitting positions. In addition a system of holding teletypewriter conferences was developed. These conferences, called "telecons," enabled a commander or his staff at each end to view on a screen the incoming teletypewriter messages as fast as the characters were received. Questions and answers could be passed rapidly back and forth over the thousands of miles separating the Pentagon in Washington, D.C., for example, from the supreme Allied headquarters in Europe or General Douglas MacArthur's headquarters in the Far East.
During the latter years of the war, new and improved communication and electronic devices came forth from research and development in ever-increasing numbers. A new long-range electronic navigation device, known as loran, used for both naval vessels and aircraft, was developed, as were short-range navigational systems, called shoran. Combinations of radar and communications for the landing of aircraft in zero visibility were perfected. One such system was the GCA, or ground-controlled approach system. Combinations of radio direction-finding, radar, and communications systems were developed and used for ground control of intercept aircraft--the system called GCI (ground-controlled intercept). Radio-controlled guidance of falling bombs enabled an operator in a bomber to direct a bomb to the target. Electronic countermeasures made their appearance in the form of jamming transmitters to jam radio channels and radar, navigation, and other military electronics.
The military services learned well from their wartime experiences the importance of scientific research and development in all fields, including communications electronics. Advances were made in the communication capacity of wire and radio relay systems and in improved electronic aids for navigation. Measures to provide more comprehensive and more reliable communication and electronic equipment continued to be stressed in the armies, navies, and air forces of the major powers.