Company then also began producing magneto-striction echo sounding equipment, for measuring 
water depth, which gradually replaced the Fathometer in Naval vessels, and the RCA produced 
‘two echo ranging equipments which were used experimentally. 
The handful of zealous Sonar workers were now busily engaged in continuing developments 
to improve Sonar and investigating Sonar’s operating medium - the ocean. Information was 
needed concerning the loss in intensity of sound traveling between two points, reflecting prop- 
erties of targets, character and masking properties of extraneous background noises, effects 
of temperature changes, and methods of making absolute underwater Sound measurements. Data 
on these factors was essential to the design of efficient equipment. NRL began studies in detail 
of these water propagation characteristics on a purely Scientific basis. The Bureau of Ships, 
NRL and fleet units began discussions of sound-in-water phenomena with the Scientists of the 
Woods Hole Oceanographic Institution and the Scripps Institute of Oceanography. 
In'1934 two destroyer divisions and two submarines based at San Diego were engaged in 
training of Sonar operators and formulating Sonar Tactics Doctrine to prescribe the basic 
procedures of employing Sonar in convoying. Each Sonar may begin searching a given Sector 
by listening on the transducer, moving it a few degrees, listening, etc., until the sector is cOv- 
ered, each escort continually sweeps his assigned sector of the ocean. Ifa submarine’ s noise or 
propellers are heard, or it is suspected that the submarine is lying-to, the Sonar “ping- -echo” 
feature may be employed. Sometimes the search is conducted entirely by pinging. Once an echo 
is received, several escorts usually maintain Sonar contact with the submarine while they attack 
by Sonar navigation, The submarines’ Sonar can usually hear pings at distances greater than 
from which ping echoes can be obtained; thus if he remains distant (where pings do not reach) 
or moves further away, his attack on the convoy is frustrated, if he moves toward the convoy the 
pings .contact him and the submarine finds itself on the spot. lf the submarine fires torpedoes, 
they may be heard by Sonar and perhaps avoided by quickly turning the surface ship. 
Early in 1939 it became apparent that training of personnel could not be handled as a by- 
product of engineering and tactical tests. Consequently the U.S. Fleet Sonar School at San Diego 
was established in order to increase training facilities. The Radio and Sound School at NRL also 
expended its technical training in Sonar. Various instructional equipments including electronic 
anti-submarine attack teachers for duplicating seagoing training were being developed and used. 
To provide more equipments and training, the Radio Corporation of America was placed under 
contract by the Bureau of Ships and commenced production of echo ranging Sonar in the summer 
of 1939. The value of Sonar was becoming keenly appreciated. 
Thus by 1939 Sonar had progressed remarkably since 1918. The capability of World War 
I listening apparatus was limited to indicating the presence and general area of U-boats that 
were underway. Now, as the World was on the brink of another war, in which the U-boats were 
to take a major role, we had ships equipped with Sonar systems capable of detecting U-boats 
whether they were surfaced, submerged, underway or lying still; furthermore, we could tell their 
bearing, distance, and almost exact location. This achievement was literally due to a few individ- 
uals whose zeal was unthwarted by many disappointments: occasioned by lack of adequate funds 
for research and development, insufficient appropriations to equip more than about a dozen ships 
per year, and limited fuel allowance which prevented ships from conducting more tactical train- 
ing exercises. The naval officers who pioneered Sonar pleaded in vain to have these deficiencies 
adjusted. In spite of this, their enthusiasm and perseverance resulted in Sonar being one of the 
few exceptions to the generally accepted rule that new wars are Started with the equipment in 
use when past wars ended. The Navy’ S job of “preparing for war in peacetime” had been done 
in the Sonar field to the limit of available appropriation. 
When World War I began, neither Axis nor Allies were prepared for intensive submarine 
warfare, The Germans had only about twenty 500-ton and ten 750-ton oceangoing U-boats. The 
British had fitted their “ASDIC (British word for Sonar) on 165 destroyers, 34 small patrol 
craft, and 20 trawlers, and the United States had about 60 destroyers fitted with echo ranging 
Sonar. Contracts were made with the Submarine Signal Company to increase production of echo 
ranging equipments in order to equip our old destroyers within six months. 
EAs A-2405 
