182 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
tween the original type of set and this new set are described in 
some detail in succeeding paragraphs. 
The production of several thousand of the airplane wireless tele- 
phone sets in the brief space of a few months involved many prob- 
lems of an extremely unusual and difficult nature. As an example 
may be cited the production of the vacuum tubes required for use in 
the sets. Prior to the war the vacuum tubes had never been pro- 
duced at rates greater than a few hundred tubes per week. At the 
time of the armistice the production of these tubes in one factory 
alone was in excess of 25,000 per week, the largest part of which was 
intended for use with the airplane wireless telephone sets. The prob- 
lem of devising methods for testing the completed sets involved the 
development of unusual testing facilities and the creation of a large 
organization of inspectors to handle the sets as rapidly as they were 
delivered from the factory. It was obviously impossible to test each 
completed set in an airplane before considering it as finally accepted, 
so that the formulation of the testing specifications involved the de- 
velopment of tests which would approximate the conditions encoun- 
tered on airplanes and at the same time would be adapted to factory 
methods of testing. 
Before the development of the airplane wireless telephone sets had 
proceeded even to the point where success was assured, it became 
apparent to those involved in the work that the production of a satis- 
factory set was by no means the complete solution of the problem. 
The successful use of the equipment would undoubtedly require a con- 
siderable amount of training of the aviators and a very considerable 
period of experiment with the trained aviators using the equipment 
before its limitations and its possibilities could be even approximately 
determined. Accordingly preparations were made in advance of the 
delivery of the first production sets, to institute a course of training 
which was intended both to familiarize the aviator with the actual use 
of the set and to work out the method of use; in other words, the 
tactics of a voice-commanded airplane squadron. As early as May, 
1918, groups of airplanes using the wireless telephone sets were being 
trained in the use of this equipment and were being drilled in the 
evolutions which the equipment made possible. In June, 1918, a 
squadron of 39 airplanes, equipped with wireless telephone sets, went 
through a course of drill in the air in such a manner as to demon- 
strate the remarkable possibilities of a voice-commanded squadron. 
Subsequently the training of aviators in the tactics of “ V. C.” flying 
progressed at a rapidly increasing rate, so that at the time of the 
signing of the armistice many thousand flights had been made. The 
record of these flights is a glowing tribute to the efficiency of the 
design of the airplane wireless telephone sets, which performed in 
such a manner as to give far less trouble than the airplane engine. 
