Attack Aids, 



Various types of attack plotters were worked on by the 

 General Electric Company p Armour Institute and HUSLo The 

 Antisubmarine Attack Plotter developed by the General Electric 

 research workers was adopted and widely usedo This was an 

 electronic device by which the relative positions of own ship 

 and target were shown on a cathode ray Plan Position Indicator 

 and firing time was indicated by a system of lights,, 



Sonic Listeni ng^Gear , 



It had been recognized shortly after the outbreak of the 

 Pacific war that there was need for sonic listening equipment 

 capable of detecting sounds produced by stationary or slowly 

 moving surface craft and of indicating at the same time any 

 detectable noises produced by the submarine Itself At that 

 time the standard listening equipment on U. So Navy submarines 

 was designed for the reception of sound in the supersonic fre- 

 quency range „ The use of gear receiving sounds in the sonic 

 range had earlier been abandoned because of the poor direc- 

 tionality and limited frequency response of hydrophones then 

 available, the high submarine self-noise levels in the sonic 

 frequency range , and the lack of adequate control of amplifier 

 frequency response characteristics* 



Experimentation on hydrophones for antisubmarine patrol 

 craft had resulted in the development of toroidal and straight 

 magnetostriction hydrophones with good wide band frequency 

 response characteristics and with sufficient directivity to 

 ensure noise discrimination and to determine accurately the 

 bearing of the sound source,, Tests with a hydrophone of this 

 type showed that listening was possible at useful speeds 

 Development work accordingly was undertaken at the New London 

 Laboratory , one of the first problems being to make the. 

 hydrophone uni-directional instead of bi-directional 



As ultimately developed, bhe JP equipment used a three- 

 foot straight magnetostriction hydrophone mounted topside 

 near the after-end of the forward torpedo room,, The hydro- 

 phone was rotated by means of quiet hand-training. mechanism 

 and its output was amplified by means of a high gain sonic 

 amplifier having a normally flat frequency response char- 

 acteristic and incorporating a series of high pass filters „ 

 Monitoring at the amplifier was accomplished by means of 

 headphones or a loudspeaker. Numerous patrol reports sup- 

 ported the evidence of extensive tests and showed that the JP 



106 



