180 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
ing to the use of the vacuum tube in wireless telephone apparatus. 
As a result of these experiments, the transmission of speech from 
Washington, D. C., to Paris and Honolulu by wireless telephone oc- 
curred during the year 1915. In these experiments the vacuum tube 
was used as a radio frequency generator, a modulator, a detector, and 
amplifier. 
The possibilities of the vacuum tube for wireless telephony. hav- 
ing been partly disclosed by the above experiments, the Navy De- 
partment became actively interested in the development of wireless 
telephone apparatus for use on battleships. Experimental sets were 
developed by the Western Electric Co. and extremely promising re- 
sults were secured. The Signal Corps was likewise interested in the 
development of apparatus for the Army, but experiments had not 
proceeded to the point where any satisfactory apparatus had been 
developed prior to the declaration of war by this country. 
FIELD OF MILITARY APPLICATION. 
Prior to the beginning of the European War the use of wireless 
telegraphy in military operations had been limited to an extremely 
narrow field, while wireless telephony had been used to an entirely 
negligible extent. The communication requirements for the armies 
engaged in the trench-warfare style of conflict emphasized the need 
of radio communication, and accordingly the extent and variety of 
the apparatus for wireless telegraphy increased rapidly. At the 
time this country entered the war wireless telegraphy comprised an 
extremely important and extensive part of the communication sys- 
tems employed on the western front. ‘The development of wireless 
telephony, however, had not proceeded to the point where satisfac- 
tory apparatus was available for use by the military forces. The 
particular field which most urgently required its use was the airplane 
communication system. The limitations imposed on the use of wire- 
less telephony, such as greater weight and complication of the appa- 
ratus and complete lack of secrecy, had hitherto prevented favorable 
consideration of wireless telephony as a substitute for wireless teleg- 
raphy. The particular requirements of the airplane communication, 
however, introduced certain advantages which more than compen- 
sated for these factors and made telephony much more desirable 
than telegraphy. The controlling reason for the use of the wireless 
telephone lay in the fact that its use eliminated the necessity of a 
knowledge of the telegraph code on the part of the aviator. An 
additional advantage lay in the greater speed with which the tele- 
phone transmission can be effected. 
Inasmuch as the airplane wireless telephone set comprises not only 
the most interesting example of the use of wireless communication 
