Tactical Radios of the AEF

Truck-mounted SCR-50 Radio Station

The U.S. Signal Corps was far behind other nations in radio or wireless technology when arriving on the battlefields in France. The Allies had been using radios in combat since 1914 and were in the process of replacing their quenched-spark radios with more reliable and rugged systems incorporating triode tubes. Nevertheless, during the war the U.S. Army Signal Corps was blessed to have the services of two of the greatest radio innovators of the 20th century.  General George Squiers, already an internationally recognized scientist and inventor, was the AEF's Chief Signals Officer and Edwin Armstrong led the effort of the AEF's Paris laboratory to equip aircraft with radio capability.  

The radio was a significantly new piece of technology in modern armies of the twentieth century. The Signal Corps had two radio systems on hand when America entered the war, the pack radio set, SCR-49 and the wagon radio set, SCR-50. Both radios were large, cumbersome, high power quenched-spark transmitters with crystal receivers.  Due to the early technology of these radios, they were used as radiotelegraphs, transmitting Morse code rather than voice.  

Pack or "Mule" SCR-49 Radio Set (Signal Corps Museum)

The pack radio consisted of the radio, cables, antenna, mast, and hand generator. It was broken down and transported using two or three mules (or horses) and unpacked and operated within two-and-a-half minutes. It had a range of 20 to 30 miles, depending on the terrain and atmospheric conditions.  The wagon radio set consisted of the radio, cables, engine, dynamo, antenna, mast, guy ropes, and counterpoise. Due to its weight and bulky size, the wagon radio set required a truck or tractor for transportation. It had a range of 150 to 250 miles and could be unpacked and begin operation within ten minutes. A tactical radio capable of transmitting voice was fielded only after the war had ended in November 1918.  Consequently during the main fighting period of the AEF, May to November 1918, The Signal Corps relied primarily on French and some British radio equipment due to the U.S. Army’s slow development in radio technology.

However, in the field of radio, the Signal Corps made its greatest gains during the Great War.. Crucial to the improvements in radio was the use of vacuum tubes, replacing the earlier spark-gap radios. Although spark-gap radios were useful, the vacuum tubes allowed continuous wave (CW) to be practical in battle. By war's end, the Signal Corps had four improved T.P.S. (earth telegraphy) sets, three types of CW sets, a radiotelegraph set for tanks, and radio operating and repair trucks. 

The More Advanced SCR-54 Developed and Operated During the War

Another critical improvement in battlefield radio communications was the invention of the SCR-77; a two-way radio loop set (spark-gap). A common problem with radios during the war was that their antennas made great targets for the enemy (and therefore made it dangerous to be an operator). This new radio set, which was send-and-receive radiotelegraphy, laid the receiving antenna on the ground, while the transmitting antenna used a small loop connected to the spark-gap transmitter. This radio had a range of six miles, could transmit on two wavelengths, and was transported in three sections, each weighing less than 30 pounds.  The SCR-77 radio demonstrated great improvements in both survival of the operator and usefulness in close ground combat. The great leaps made in radio technology during the war paid dividends when America entered her next war 23 years later

Source: THE EFFECTIVENESS OF THE U.S. ARMY SIGNAL CORPS IN SUPPORT OF THE AMERICAN EXPEDITIONARY FORCE DIVISION AND BELOW MANEUVER UNITS DURING WORLD WAR I by Maj. Douglas J. Orsi, U.S. Army