* Along with radar, electronic warfare systems, and radio navigation systems, World War II also saw the introduction of improved radio communications systems, including radios small enough to be carried by infantrymen, radio relay systems, and "secure" radios for spies.
* Voice radio, as opposed to wireless telegraphy, came into widespread use in the 1920s. Initially, voice radios were based on amplitude modulation (AM), in which the voice signal was directly mapped into changes in the amplitude of the radio signal. AM radio was an effective technology, but it was prone to environmental interference or "static", and in the 1930s the American inventor Edwin Armstrong, one of the fathers of modern electronics, developed a voice radio scheme based on frequency modulation (FM), in which the voice signal was mapped into changes of frequency from the radio carrier frequency, substantially reducing interference.
FM was basically still a leading-edge technology at the beginning of the war. The Connecticut police force conducted tests of a two-way FM radio system in October 1939. The radio -- designed by Daniel Noble, a professor of electrical engineering at the University of Connecticut and built by the Link Radio Corporation of New York City -- offered clear communications over distances as long as 40 kilometers (25 miles). The evaluations were successful, and in 1940 the state of Connecticut awarded a contract to Link to implement a statewide mobile FM radio system. The contract attracted the attention of the US military, and in October 1940 a group of more than a dozen US Army Signal Corps engineers and officers from Fort Monmouth, New Jersey, went to Hartford, Connecticut, to inspect the Link system.
The Signal Corps officers were as impressed by the Link FM radio as the police had been, and two of the officers, Colonel Roger B. Colton, already mentioned as a prime mover in the prewar Army radar effort, and Major James O'Connell, began to energetically lobby for adoption of FM radio systems by US military forces.
* Along with relative noise immunity, FM radios also had the feature that if several different signals were being transmitted on one band, they would only pick up the strongest one, with the others being blocked out completely. That was not necessarily always an advantage; for example, in ground or fighter combat it could be useful to listen to what everyone in a combat team was saying over the radio. When US troops first entered combat, they were equipped with AM radios.
The "SCR-194" and "SCR-195" AM sets were the first US Army tactical radios, radios, the SCR-194 designed to be carried on an infantryman's back for use by scout teams and artillery spotters, the SCR-195 being much the same gear but adapted for vehicle mounting. These two radios were designed by the Signal Corps Engineering Laboratories at Fort Monmouth, and introduced in 1935. For whatever reasons, the two radios operated over separate bands; the SCR-194 in the 10.9 to 5.75 meter (27.5 to 52.2 MHz) range, the SCR-195 in the 5.77 to 4.62 meter (52.9 to 65 MHz) range. One suspects the separate bands were to keep, say, infantry teams and tank groups from interfering with each other, though the separate bands would have complicated support between the two -- the bands of the two radios did not overlap.
These AM backpack units were followed by the first "handie-talkie", an AM unit designated the "SCR-536", which was introduced in early 1942, being built by Galvin Electronics -- later Motorola. The SCR-536 was about 30 centimeters (1 foot) long, weighed about 2.7 kilograms (6 pounds), and had a typical range of about 1.6 kilometers (1 mile), though it might have several times that range under good conditions. It operated in the 85.7 to 50 meter / 3.5 to 6 MHz range.
The SCR-536 was a neatly self-contained unit, containing electronics, batteries, microphone and earphone, and a collapsible antenna. The handie-talkie was often the first radio ashore in amphibious operations, where it was carried in a sturdy waterproof bag by the first assault wave to provide situation reports and call in naval gunfire support. The SCR-536 was first used in Allied landings in Sicily in 1943, where it was captured by the Germans and evaluated. The Germans were impressed by the device, describing it as "extremely effective". However, the initial SCR-536 design was not really designed for tropical operations, and in the jungle fighting in the South Pacific the handie-talkies often failed due to corrosion caused by high humidity and temperatures. Treatment kits were provided to extend their useful life to about a month. A total of about 130,000 SCR-536s was built in all.
Since AM radio could pick up multiple transmissions on the same band, it remained standard for aircraft through the war, though early HF AM gear was had too few channels, making fighter control difficult. Improved VHF AM with larger numbers of channels proved more adequate. The British-designed "SCR-522", mentioned earlier, was built in very large quantities by Bendix for use with American aircraft. The SCR-522 provided four channels in the 3 to 1.92 meter (100 to 156 MHz) range.
* The first US military FM radio to go into operation was the "SCR-508", which was big and heavy and so only used on jeeps, tanks, and other vehicles. It was based on Link Radio Corporation designs, with development performed by Bell Laboratories and Western Electric for the Army Signal Corps. It operated in the 15 to 10.75 meter (20 to 27.9 MHz) range, and was introduced in March 1942. The SCR-508 was followed shortly after by the "SCR-608", which was almost identical except that it operated in the 11.1 to 7.71 meter (27 to 38.9 MHz) range. Almost every Sherman tank mounted such an FM radio, giving tank commanders excellent communications with artillery batteries. The Marines and Navy used them for amphibious operations.
In early 1943 the Signal Corps introduced the first infantry FM backpack radio, the "SCR-300", which weighed 18 kilograms (40 pounds), had a range of 16 to 32 kilometers (10 to 20 miles), and operated in the 7.5 to 6.25 meter (40 to 48 MHz) range. The SCR-300 first went into combat during the landings at Anzio in Italy in January 1944, and proved itself in battle during the rest of the war as a reliable and effective piece of equipment.
BACK_TO_TOP* The Signal Corps also developed radio relays to stretch the range of tactical radio communications. The scheme had its origins in the North Africa campaign in 1943, when Motorola police radios were pressed into service to provide a one-channel teletype link from Algiers to Tunisia, a distance of 640 kilometers (500 miles).
Formal US Army radio relay systems were introduced late in that year. They were generally designated "AN/TRC", and were simply called "antracs". "AN/TRC-1" was the result of an informal "garage job" development effort by engineers at the Signal Corps Camp Coles Signal Laboratory in New Jersey, with assistance by Link Radio. Field evaluations of AN/TRC-1 prototypes were conducted in New Jersey and on the coast of Maine in 1943.
Before the AN/TRC relay radio systems became available, telephone wires had to strung to implement long-range communications link. Setting up such long wire systems was a laborious, time-consuming, and expensive chore: laying 160 kilometers (100 miles) of telephone line took 2,000 men almost ten days. In contrast, an AN/TRC relay system could cover the same distance using two terminals and three repeaters, and could be set up by 44 men in three days. Furthermore, such an AN/TRC system required only a third of the transport capability needed to ship a wire system to a combat zone.
The AN/TRC-1 was followed by the similar "AN/TRC-2" and "AN/TRC-4". They could carry one voice channel or four teletype channels and operated in the 4.29 to 3-meter (70 to 100 MHz) range. The AN/TRCs were available in time to serve in the Normandy invasion and the invasion of the Philippines, and saw extensive use through the rest of the war.
Four channels was not enough, and so the Signal Corps worked with Bell Telephone and RCA to develop the "AN/TRC-5" and "AN/TRC-6" radio relays. These were derived from the experimental British "X10A" wireless set, which went into British service as the "Number 10" set. The X10A featured eight channels, transmitted with pulse amplitude modulation using time division multiplexing, or "time-slicing", with different conversations cut into slices that were sent in an alternating cycle.
BACK_TO_TOP* One interesting wartime application of FM technology was the "Joan / Eleanor (J/E)" radio system, developed for the Office of Strategic Services (OSS) by a young engineer from Ohio named Al Gross.
Communication with secret agents operating in enemy territory was a dangerous business, since enemy counterintelligence could use radio direction finding to pin down the signal and catch the agent working the transmitter. One clever set of agents fooled the Germans by buying a wine cart with an oversized barrel on it, and putting a wall inside it so that the bottom held wine and the top held one of the agents with a radio. By moving around, they were able to avoid being located by direction finders.
That was not a trick that could be used by every agent, and Gross built a small portable radio, Eleanor, that featured a highly directional beam that pointed up, to a circling aircraft equipped with a complementary radio, Joan, and a wire recorder to store the message. Eleanor and Joan communicated with each other around 1.15 meters (260 MHz).
Outside the vertical beam, Eleanor was invisible to ground-based radio direction finding equipment. Encryption was unnecessary, except for the most critical messages. Hearing a specific agent's voice provided an additional degree of security, and also gave the agent's handler a feel for the agent's emotional state.
The two radios derived their names from the OSS practice of assigning projects female names chosen at random as a security measure. Eleanor weighed only 1.8 kilograms (4 pounds), including batteries and a collapsible antenna, and the whole kit neatly fit into a soft carrying case that could be easily concealed. By the standards of the time, it was a technological wonder. The J/E system was first put into operational use in the Netherlands in November 1944. Twelve intelligence teams using J/E were placed into Germany in early 1945, and the system proved highly successful.
Al Gross went into commercial production of FM two-way radios through his Citizens Radio Corporation of Cleveland, Ohio, in 1948, but his FM radios never seriously caught on. His patents ran out in the mid-1960s. A decade later, AM CB radios became a national fad; it seems that Gross was possibly ahead of his time.
BACK_TO_TOP* Underlying the new technologies used in World War II were the organizational structures that developed them. The British created the TRE and other organizations, and the United States was possibly the most far-sighted of all the combatants by establishing the powerful OSRD to direct research and development activities at the highest level. The OSRD promoted cooperation between its own agencies, universities, and industry for industrial technology development, and this network would become the basis of what would be called the "military-industrial complex" after the war.
In Germany, in contrast, Nazi management of their high technology assets was haphazard and indifferent. Hitler's antisemitism drove many bright Jewish minds from Europe to Britain and particularly the United States, where some helped make the atomic bomb a reality. "Victory fever" also plagued the Nazis in 1940 and 1941, leading to overconfidence and a de-emphasis of research programs. Bureaucratic factionalism kept different German research labs working at cross purposes, and valuable technical experts were drafted by the military and sent off to combat as infantry. The situation was even worse in Japan.
Overwhelming American manufacturing capability was also a major factor in the defeat of the Axis. Even before American entered the war, the US was ramping up to become what US President Franklin Delano Roosevelt called "the arsenal of democracy", and by 1943 American manufacturing and raw materials were helping bolster the other Allied powers in their own war efforts. Axis industry could not compete, and under heavy air attack their industrial production eventually withered and collapsed. In the postwar period, new technologies would be refined, and though a single-minded focus on technology as the solution to military problems would prove short-sighted, technology would still become a pervasive underlying reality in military operations.
* The RRL was formally disbanded on 6 December 1945, with the end of the Rad Lab following on 31 December 1945. Part of the Rad Lab was retained by MIT as a basic-research organization. A number of the best minds in the Rad Lab, such as Luis Alvarez, had quietly departed long before that time to work on the supersecret atomic bomb project at Los Alamos, New Mexico. In fact, Alvarez witnessed the Hiroshima bombing from an observation aircraft.
I.I. Rabi had made sure that everything the Rad Lab had done was documented before the end, partly to demonstrate what the organization had been doing with all the money pumped into it. The writing effort began in the fall of 1944, ultimately resulting in 28 volumes, with contributions by 49 authors. The work was edited by Louis Ridenour, who had headed the SCR-584 team. There were loud complaints about fiddling with paperwork when there was a war on -- but it was either write it down, or forget everything.
That proved wise, since military radar and countermeasures research went mostly dormant for a few years, the main work being a few projects at the service facilities like NRL. However, the Rad Lab documents and the expertise built up during the effort did spark a wide range of commercial efforts, with one result being the Raytheon "Radar Range", which would eventually evolve into the modern microwave oven.
The beginning of the Cold War a few years later reawakened military interest in the field, and the information left behind by the Rad Lab proved very useful. The Rad Lab was more or less revived in the 1950s as the "MIT Lincoln Laboratory", which survives to the present day. The British research establishment at Malvern never went away in the first place and still exists, though it has gone through many name changes.
Many of the veterans of the Rad Lab effort went on to distinguished careers in related fields. George Valley became one of the prime movers behind the "Semi-Automatic Ground Environment (SAGE)", a computerized air-defense network for the defense of North America using huge IBM vacuum-tube computers. Jerome Weisner would become the presidential science adviser in the Kennedy Administration. Ivan Getting, who had helped develop the SCR-584, would later help create the Global Positioning System satellite navigation constellation. Some junior workers at the Rad Lab and other organizations in the radar effort would rise to prominence in the postwar period and make their own contributions to science and technology.
As far as the British effort went, Taffy Bowen worked on radio astronomy in Australia, while Bernard Lovell established a name for himself in the field in the UK. With wartime secrecy gone, Watson-Watt heavily promoted himself as "the inventor of radar". He took credit for a wide range of things, much to the annoyance of other veterans like Taffy Bowen, who knew that other people had generally done the real work.
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