to be dropped from a search plane when it knew or suspected 

 that a submerged submarine was in the area. 



ERSB consisted of an underwater listening device which 

 picked up the sounds of a submarine and transmitted them to a 

 radio set which then sent the sound to the listening airplane . 

 The buoy's radio range was dependent on the altitude of the 

 plane c Frequency-modulated radio transmission was used in 

 view of the stringent noj.se suppression requirements and to 

 obtain freedom from interference , . Buoys could be operated 

 on any of six radio frequencies Multi-channel reception in 

 the receiver made it possible, by operating a selector switch, 

 to listen to any desired buoy„ 



The radio sonobuoy met an urgent need, With dishearten- 

 ing frequency planes and blimps sighted enemy submarines only 

 to see them mr ddeningly crash-dive to safety before a suc- 

 cessful attack could be launched,, ,. By the time surface ships 

 arrived— usually a matter of hours, or even days — it was,, more 

 often than not, too late to regain contact by echo-ranging <> 

 The Navy's antisubmarine experts' qutllried the problem to the 

 underwater sound group at Columbia University's laboratory 

 at New London, where W, Bo Snow, assisted, by" Jo W, Horton, 

 was placed in charge of the new projects Later,, A', Go 

 Wamback was made supervisor, with J, A, Barkson as his prin- 

 cipal assistant. 



The first tests were designed to show whether or not the 

 fundamental idea was practicable , , Two convoy type buoys 

 were used and were placed in the water by a launch,, Then 

 with a submarine serving as a submerged target, listening 

 tests were conducted aboard the blimp K>5 by means of a radio 

 receiver installed for the purpose. As the blimp circled 

 overhead the submarine's propeller sounds were clear and dis- 

 tinct in the headphones.; Radio reception continued good as 

 the range was increased. Then the submarine also moved away 

 from the buoyj and still its noise could be heard and iden- 

 tified by listeners aboard the blimp. Obviously,, the basic 

 idea was sound. 



Encouraged by these- results the research team went to 

 work, J, To McNary and W, L, Widlar rushed the Mark I trans- 

 mitter model to completion - producing what amounted to an 

 entire frequency modulation broadcasting station on a round 

 chassis less than five inches in diameter and under ten 

 inches long, R, A, Fox, basing his work on the electrical 

 features of the convoy unit, was striving to complete a 



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