When on May 22, 1917, Gen. Squier, the Chief Signal Officer of the Army, called upon the scientists to develop at once an airplane telephone, he was not only introducing them into what was to many of them a new field, but he was asking them to produce what the science of Europe had been unable to create in nearly three full years of acquaintance with the successful ground system, although the needs of airplane fighting demanded this invention as they demanded almost nothing else.
It will thus be seen that when we began this development as a war measure we had a considerable basis of experience to work upon. The Army had established the foundation of operation on the airplane, made a study of the tactical requirements, and knew what it wanted. The Western Electric Co. in 1914 and 1915 had conducted extensive experiments with the radio wireless telephone at a ground station at Montauk, Long Island, and had played an important part in the long-range experiments at the Arlington station. There had been wireless voice communication before this time, but the apparatus and systems perfected at Montauk set the standard on which all subsequent development was built. The French Scientific Mission and other officers of the allies had arrived and enabled us to check up what had been done abroad and to confirm or modify our ideas of the tactical requirements.
At the conference with Gen. Squier in May was Col. Rees of the Royal Air Force of Great Britain; Col. C. C. Culver, United States Army, then a captain; and F. B. Jewett and E. B. Craft, respectively the chief engineer and the assistant chief engineer of the Western Electric Co.
At this meeting Gen. Squier outlined the future of the part the airplane was to play in the war, and pointed out how invaluable would be a successful means of communication between battle planes when flying in squadron formation. Mr. Jewett had received his commission as a major in the Signal Corps, and he was ordered to take charge of the work of developing radio communication for aircraft.
Capt. Culver had taken part in the 1910 experiments and discussions, and since 1915 had been conducting the Army development of airplane wireless at the aviation school at San Diego, Calif. He was detailed to work with Maj. Jewett and his engineers, bringing to their assistance the result of his experience and the point of view of the trained military man and the aviator.
The first development was carried on in the laboratories of the Western Electric Co. on West Street, in New York. Men and materials were drafted from every department of the company, and the laboratories were soon seething with activity. In a few weeks the first makeshift apparatus was assembled, and the first practical test of a radio phone on an airplane was made at Langley Field at Hampton, Va., less than six weeks after the Signal Corps had given the go-ahead. Three employees of the Western Electric Co. on that day established telephone communication between an airplane in flight and the ground. A few days later the first apparatus produced successful communication between planes in the air.
It is not possible here to go into a technical description of the wireless telephone. The most vital part of the apparatus, however, and the essential factor in airplane wireless telephone communication is a vacuum tube containing an incandescent filament, a wire mesh or grid, and a metal plate. By means of electrical current the wire filament is heated to incandescence. The tube has the property of receiving the energy of the direct current of a dynamo and, through the medium of the wireless antennæ, of throwing it out into space as a high-frequency alternating current. Such is the sending tube. A modification of the same tube picks up from the antennæ the high-frequency alternating vibrations from another sending apparatus and transforms them into direct current, carrying the sound waves of the human voice along with them.
The design of the radio apparatus itself was relatively simple for the experts who had undertaken the work, for the company had already developed some highly successful forms of vacuum tubes, and it was an easy matter for these technicians to assemble tubes with the necessary coils, condensers, and other apparatus of the transmitting and receiving elements and produce a system of such small compass that it could be carried on an airplane. But working this apparatus under ordinary conditions in the quiet laboratories and in a swift-moving and tremendously noisy airplane were two different propositions.
One of the first problems was to design a comfortable head set which would exclude all undesirable noises and admit only the telephone talk. A form of helmet was finally devised with telephone receivers inserted to fit the ears of the pilot or observer. Cushions and pads adjusted the receiver to the ears, and the helmet fitted close to the face so as to prevent as far as possible the transmission of undesirable sounds either through the ear passages or through the bony structure of the head, these bones acting as a sort of sounding board. The designers finally developed a helmet that solved this portion of the problem.