Judson Mead and Mr Q Co So Pear sail In August 1941 the group 

 was joined by Dr Q Do Go Co Hare,, who later became laboratory 

 director, with Mr„ Wo Bo Lodge as assistant director* 



f 



The detector element used in MAD had previously been in- 

 corporated in a magnetic mine device developed, under a con- 

 tract with NDRC's Section D-3, by Mr. V, V» Vacquier of the 

 Gulf Research and Development Company under the direction of 

 Dr„ E, Ao Eckhardto The latter had brought the detector 

 element to the attention of Division 6 and ultimately another 

 contract between NDRC and the Gulf Laboratory was drawn up a 

 This contract was later supplemented by contracts with the 

 Western Electric. Company and the General Electric Company for 

 work on various types of magnetic detectors „ As the work 

 grew, so the staff grew,, and by the end of 1942 a total of 

 160 people were working on the project and by the end of 

 1943 more than 350 . 



The operation of MAD depends upon measuring the distortion 

 in the magnetic field of the earth caused by the presence of 

 the ferro-magnetic mass of a submarine „ The magnetic field of 

 the earth has a total intensity of about 60,000 gammas, one 

 gamma being equal to 10- gauss „ The distortion of this field 

 due to the presence of a submarine at a distance of a few 

 hundred feet is of the order of only a few gamma s 



A major problem faced by the researchers resulted from 

 the fact that the earth's magnetic field is a vector quantity* 

 Thus relative motion between it and the sensitive axis of the 

 measuring device will produce indications of changes in field 

 intensity o These spurious indications must either be neutral- 

 ized or the effects of the relative motion between the meas- 

 uring device and the earth's magnetic field must be eliminatedo 

 False signals may also be created by the magnetic field pro- 

 duced by the aircraft itself 



How successfully this major problem was solved is in- 

 dicated by the fact that the MAD equipment, as finally 

 developed, had a background noise level of only some 0*2 gamma 

 under conditions of reasonably straight and level flight and 

 of not more than a few gammas under conditions of rapid 

 maneuvering* Thus the equipment was capable, in even flight, 

 of detecting a submarine where the magnetic anomaly produced 

 by its presence was only a few gammas 



An experimental device constructed by the Sperry Gyro- 

 scope Company according to the Gulf Company's specifications 



88 



