SONAR - DETECTOR OF SUBMERGED U-BOATS 
During the War’s most critical period the Allies proclaimed, “History is repeating itself, 
as in 1914-1918, so in 1939-1942; although we shall not win the War by defeating the U-boat, we 
shall assuredly ‘lose the War if we do not defeat them”. 
We just barely won the U-boat warfare. Nearly 1000 enemy submarines were sunk, many 
hundreds more damaged and thousands of their attacks frustrated because we were able to detect 
and locate them whether surfaced, submerged, underway or lying in wait. The Axis tremendous 
respect and grave fear of our detection was declared by Gross Admiral Doenitz’ top secret letter 
of 14 December 1943: “For some months past the enemy has rendered the U-boat war ineffec- 
tive. He has achieved this objective, not through superior tactics or strategy, but through his 
superiority in the field of science; this finds its expression in the modern battle weapon - detec- 
tion. By this means he has torn our sole offensive weapon in the war against the Anglo-Saxon 
from our hands”, 
In the majority of our attacks on U-boats, they were detected and located by SONAR. To 
date, Sonar has been the only effective method of detecting completely submerged Submarines; 
other methods such as Radio, Radar, Infra-red, etc., have proven ineffective because their ef- 
forts stop at the surface of the sea. Sonar s consistent effectiveness was a major factor in the 
defeat of the U-boat, the U-boat which could have prevented Allied victory. The Navy has main- 
tained its secret of Sonar throughout and between both wars. Its development has been an unspec- 
tacular, long, Slow, steady conquest over the physical elements of the sea continuing in both war 
and peace. The word SONAR abbreviates SOund, Navigation And Ranging, which includes all 
types of underwater sound devices used for listening, depth indication, echo ranging, location of 
obstacles, etc. 
The first popular use of U/W sound was confined to navigational purposes with apparatus 
produced by the Submarine Signal Company about 1902. A clapper type pneumatic bell, installed 
on light-ship vessels, transmitted sound waves which were received by ships having a micro- 
phone on each bow. A rough estimate of the sound’s direction was obtained by shifting headphones 
alternately to port and starboard microphones. The bell’s low frequency could hardly be distin- 
guished from various ship noises, consequently in 1907 the Submarine Signal Company produced 
as replacement the 540 cycle Fessenden oscillator which was essentially an electro-magnetic 
loudspeaker which vibrated against the water. 
These equipments were useless in detecting any of the U-boats at sea during the first half 
of World War I. By 1916 the United States Navy had developed and installed an acousticat# listen- 
ing device designated as “SC” which consisted of 2 three-inch diameter rubber nipples mounted 
five feet apart on a T-shaped hollow pipe which terminated in a stethescope. The T Ss were 
hung over the side or protruded through the bottom of Sub Chasers, which searched by stopping 
to listen, proceeding a few hundred yards, stopping and listening again, etc. Only a rough esti- 
mate of a target s location could be obtained; however, teamwork and triangulation by several 
anti-Submarine vessels provided location for depth charge attacks. The charges were dropped 
over large areas with only small hope of scoring a kill, or of forcing the U-boat below periscope 
depth to prevent its aiming torpedoes or tracking ships. U.S. submarines also had the SC, the 
German U-boat listening device was effectively identical, and the British detectors were similar. 
In 1917 the convoy system was adopted and sound equipped anti-submarine vessels escorted 
convoys through U-boat infested waters. From April to October 1917, about 1501 ships in 99 
convoys had lost only 10 ships to the average 40 U-boats operating continually at sea during the 
last half of the war. 4,837 Allied merchant vessels (11,000,000 gross tons), or about 95 ships 
per month, were lost throughout the fifty-one months. These losses would have been much higher, 
had it not been for about 3,000 Allied assorted sound equipped craft which frustrated many attacks. 
178 U-boats were sunk. 
In the closing months of World War I the Allied Submarine Devices Investigation Committee 
(ASDIC) was formed to obtain from science and technology more effective underwater detection 
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