These instruments were all based en the magnetic stabili- 

 zation of the magnetometer heal without the use of any gyro- 

 scope o MAD produced a continuous trace on a moving tape and 

 distortion of the trace indicated passage near a magnetic 

 body, such as a submarine 



The principal value cf the equipment la; 1- in patrol work 

 over restricted waters such as the Straits of Gibralter, where 

 the MAD-fitted planes of Navy Squadron VP-63 and bhe blimps 

 of ZP-14 did notable work in aiding to maintain a barrier 

 against the transit of German U-boats to and from the Med- 

 iterranean, 



It was on 24 February 1944 that Planes 14 and 15 of 

 VP-63 made the first successful MAD contact with a U-boat in 

 the Straits, With MAD, they tracked and bombed it, and with 

 the aid of British destroyers and planes scored a certain 

 killo On 16 March and 15 May, two almost sure sinkings of 

 U-boats were marked up as the result cf MAD detection- 



Planes equipped with MAD were given a suitable weapon 

 through the work of another NDRC Division - Division 3, which 

 developed the retro-firing rocket bomb and its companion, the 

 retro-firing flare o Since MAD detected a submerged submarine 

 when almost directlv over the target, it was desirable to have 

 a projectile which would drop vertically. This was accomplished 

 in the retro-firing bomb, which was projected backward at a 

 speed equal to the forward speed of the plane. The two speeds 

 offset one another and the bomb plummeted downward in an ap- 

 proximately straight line. 



Despite the value of MAD in its specialized field, there 

 was still need for further devices if the airplane was to be 

 a successful hunter of submarines. And orce again the report 

 was to underwater sound 



Expendable Radio Sonobuoy . 



Out cf the work of the New London Laboratory of Division 

 6 on aircraft listening systems came the Expendable Radio 

 Sonobuoy (ER3B), The principle of the ER3B had been proposed 

 earlier for a device used for the protection of convoys, A 

 buoy could be dropped overboard from a convey ship and as the 

 convoy proceeded on its course the buoy would pick up the 

 waterborne sound of any vessel approaching from, astern and 

 transmit a warning by radio to the convoy. Instead of being 

 dropped from a ship, the Expendable Radio Sonobuoy was designed 



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