222 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
1912 emphasized the need for a means to detect icebergs in the track 
of a vessel and led to experiments in the use of subaqueous sound for 
this purpose. The instruments and methods developed, however, found 
their greatest application in measuring depths of water by subaqueous 
sound, resulting in modern echo sounding. 
During World War I the transmission of sound in sea water was 
intensively studied by the world’s foremost scientists in combatting 
the submarine menace. As a result, instrumental equipment for trans- 
mitting and receiving subaqueous sound was perfected, as well as 
instruments specifically designed for the measurement of sound travel. 
After World War I, the Coast and Geodetic Survey became interested 
in the possible use of the method to control hydrographic surveys. In 
collaboration with the War Department and the Bureau of Standards, 
experiments were conducted in the further development of the method 
and in the redesign of instrumental equipment. The method was first 
actually used in hydrographic surveying on the ship Guide off the 
coast of southern California in early 1924. It was an immediate 
success, although many details of procedure had to be perfected before 
it could be used with assurance. 
THEORY 
In radio acoustic ranging the position of a subaqueous sound source 
is determined with reference to two or more appropriately located 
sound receivers whose positions are known. Such a use of sound 
has also been called “phonotelemetry.” Angles are not utilized in 
this procedure—the unknown position is determined by measuring 
the travel times of the sound from its source to the sound receivers. 
If the effective horizontal velocity of sound in sea water is known, the 
distances from the sound source to the receiving stations may be 
determined by multiplying the travel times by the velocity, and 
from the distances the position of the sound source may be found. 
There are several ways in which the travel time of subaqueous 
sound can be used to determine the position of an unknown point: 
(a) Three or more appropriately located receiving units may be 
interconnected electrically or by radio and the times of arrival of the 
subaqueous sound at the several stations may be recorded at a central 
station. Knowing the velocity of sound, the differences between the 
arrival times may be used to derive the position of the source of the 
sound. This is known as the “differential method” and it is in 
general military use to determine the positions of enemy gun 
emplacements. 
(6) The subaqueous sound impulse may be synchronized at the 
source with a radio signal. If the elapsed times between the receipt 
of the radio signal and the receipt of the subaqueous sound are 
