equipment. U.S. activity was headed by the National Research Council, A French representative 
named P. Langevin described his experiments in producing intense underwater sounds by employ- 
ing a technique invented by Pierre Curie (discoverer of Radium). The technique involved pass- 
ing an alternating current of about 15,000 cycles per second through a crystal of quartz which 
made the quartz vibrate and produce series of compressions and rarefactions in the surrounding 
medium and thereby propagating sound waves. Langevin had sandwiched slabs of quartz be- 
tween the steel plates of his underwater transmitter which produced sound that traveled a path 
similar to the beam of a searchlight. 
Throughout World War I the Navy's major investigations had been made at its experimental 
station, New London, Conn., where important techniques were developed which, however, were too 
late to ‘enter the war. The SC acoustical air tube was expanded to contain six or more nipples on 
each bow. An electrical sonic system designated “MV” consisted of a “blister” on each bow which 
contained 12 microphones of the carbon button type that fed the sounds through electrical phase 
lines to a compensator which featured direction finding to within a few degrees. The MV and the 
SC became Navy standard installations. In September 1918 experiments were conducted with 
quartz-steel echo ranging techniques (Langevin s principles) and resulted in producing under - 
water sounds which were reflected from a moving target several hundred feet distant. 
When World War I ended the Asdic Committee was dissolved; nations and organizations 
pursued their own interests. The very few first-rank scientists who remained with the Navy, 
despite inappropriately low wages allowed by the government, have undoubtedly been extremely 
loyal in their efforts to lick an unsolved technique of grave importance. 
In 1919 the Sonar problems were transferred to the Naval Engineering Experiment Station, 
Annapolis. One important development beginning there was the Hayes Sonic Depth Finder; it con- 
tained an electro-magnet which sent sound waves to the ocean floor, received the reflection, and 
indicated the depth by a timing device calibrated basically at 4800 feet per second (speed of 
sound through water). This system was built by the Washington Navy Yard and installed in some 
Naval vessels. 
In 1923 Sonar projects were transferred to the newly established Naval Research Labora- 
tory (NRL) at Bellevue, D. C. where, in the Sound Section headed by Dr. H. C. Hayes, practically 
all of the Navy’ s peacetime Sonar research and development was carried on. The equipments 
developed at NRL in conjunction with the Bureau of Ships Sonar Section and progressively in- 
stalled in Naval vessels during peacetime, constituted the primary Sonar techniques which were 
employed throughout World War IL. 
About this time certain terminology was adopted; “Sonic” sound covered the audible range 
from 16 to 15,000 cycles (vibrations) per second, and frequencies above the Sonic band were re- 
ferred to as “Supersonic”. (Average ears respond from about 40 to 15,000). Propellers create 
sonic and supersonic sounds). 
Work on the acoustical sonic system was continued at low priority since desired signals 
(Propeller noise) suffered severe loss during transfer from water to air. Comparatively little 
signal strength is lost by transfer from water to electrical microphones and then to telephone 
head sets; therefore, development of electrical sonic systems was advanced in order to equip 
ships with the best available apparatus. However, sonic systems were generally unsatisfactory 
because various water noises caused by own propellers, own ships movements, etc., resulted in 
considerable interference. Therefore greatest emphasis was on the supersonic echo ranging 
experiments - the advantages are many; the Signal is amplified electronically (vacuum tubes), 
employment of supersonic frequencies narrows the reception range to a selective band thereby 
eliminating much of the oceans inherent sonic noises, and directivity of reception is confined to 
selective narrow pie-Sshaped sections. To these improved listening techniques are added the 
“ping-echo’ features. 
The first experimental echo ranging sets operated at frequencies between 20,000 and 
40,000 cycles per second. These Supersonic "voltages were generated by a transmitter that 
fed the transducer (combined radiating and receiving unit) which protruded through the ship’ s 
=J= A- 2405 
