v suits of all types of patterns. In a similar manner, a file 

 of 7,000 punch cards was built up to compute the probability 

 ol success for surface vessel search plans. From all these 

 studies came conclusions that were embodied in later improved 

 procedure . 



Countering the Acoustic Torpedo , 



Cne of the most important countermeasure problems dealt 

 with by Jroup M was that of finding means to combat the German 

 ac-oust'ic homing torpedo „ In 1943 rumors began to spring up 

 t] at t] r Germans were preparing to use a torpedo which steered 

 toward the noise of a ship. Soon the rumors were confirmed by 

 prisoner of war statements,, In the fall of 1943 the torpedo 

 appeared. 



Thanks to the advance warning, Group L vac air: I ' pre- 

 pared with a number of countermeasures „ This part of the 

 program was placed under the direction of Dr. E. A. Uehling. 



The problem was net a simple one. Cut of. their technical 

 knowledge the scientists had to estimate just how the torpedo 

 was controlled. A counter uer -sure effective against a torpedo 

 of one type might be ineffective against a torpedo with other 

 physical properties and might actually increase the danger 

 from torpedoes with still other characteristics. To be effec- 

 tive, a countermeasure had to be based upon knowledge of how 

 the torpedo would respond to intensity changes, how selective 

 It was in frequency, and whether it could hear sounds from 

 all directions or only from ahead. 



A large number of typical pursuit curves were somputed 

 for torpi Loes • Ltl /arying properties. The torpedo sxperts 

 of Division 6 were canvassed for their opinion as to what 

 properties the homing tcrpedo might have. These opinions, 



oupled with prisoner of war statements, narrowed the prob- 

 able- -election down to two or thre^ types. An attempt was 

 then made to find s countermeasure which would be effective 

 against all or nearly all ■■:•£ these types. 



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