RADIO RECEIVING SET, SCR-54, USING CRYSTAL DETECTOR.
REAR PANEL VIEW, RADIO TELEPHONE GROUND SET. TYPE SCR-67.
RADIO TELEGRAPH TRANSMITTING SET IN CASE.
RADIO TELEGRAPH TRANSMITTING SET WITH CASE REMOVED.
Probably the most noteworthy technical development during the war, in so far as radio communication is concerned, was the extensive use made of vacuum tubes. These "bottles," which make practical use of the electrons of the new physics and which are sometimes called audions or pliotrons, are literally marvels in the realms of engineering, and their applications are as yet hardly realized. One form was used for the reception of signals prior to the war; but the military developments, particularly in France, had so progressed that when this country entered the war they were used both for receiving and transmitting signals, and most of the more important sets depended on them. To meet this demand the services of the three foremost vacuum-tube engineering organizations of the country were enlisted, and under the direction of the Signal Corps radio engineers the progress toward satisfactory design and construction of the required types was rapid. Within less than six months standardized tubes were turned out by the quantity production method at rates sufficient to insure the requisite supply. Work was continued, however, on the development of still better types of tubes. The improvements that have been made from time to time have been incorporated in the tubes being produced on a large scale, so that tubes of recent manufacture are a great improvement over those made a year ago.
As indicative of the extent and variety of the radio development work which was carried on, there is given below a partial list of the types of sets which were completely developed and placed in production during the war period: