crude experiment the USS Kendrick was placed in dry dock so 

 that the interior of the dome could be inspected., The ex- 

 pected layer of wax- like substance was found covering the pro- 

 jector surfaces and the interior of the dome „ The deposit was 

 removed, the dome was replaced and filled with salt water. The 

 results were excellent The patterns approximated those ob- 

 tained at test stations c Similar treatment of the domes on 

 the USS LAUB and the USS MACKENZIE were equally effective, A 

 simple change in procedure of filling the domes was suggested 

 which eliminated the formation of wax deposits. This meant 

 the difference between submarine defense and vulnerability for 

 at least one convoy „ 



As eventually developed, two portable types of Sound 

 Gear Monitor known as Model OAX and Model OCP went into com- 

 mercial production and several thousand units were delivered 

 for Fleet use. Development work on a permanently installed 

 type called the Installed Sound Gear Monitor (ISGM) was 

 carried on, but not to the point of procurement of commercially 

 manufactured units „ 



Dynamic Monitor 



Helpful though it was in indicating whether the essential 

 functions of sonar gear were operative the Sound Gear Monitor 

 did not have enough panel adjustments to be used easily for 

 quantitative measurements on the over-all performance of the 

 sonar equipment under conditions of normal echo -ranging,, Thus 

 the engineers of the Harvard Underwater Sound Laboratory 

 turned to the development of the Dynamic Monitor p a device 

 designed to provide a numerical index,, called the "figure of 

 merit , " of the over-all acoustical performance of sonar echo- 

 ranging equipment o Measurements of the "figure of merit" - 

 defined as the ratio in decibels between, the transmitted inten- 

 sity of a ping at a distance of one meter from the projector 

 face, and the minimum sound intensity which will constitute a 

 detectable echo under the prevailing conditions of ambient 

 noise - permitted valid objective comparisons to be made be- 

 tween different types or conditions of sonar equipment, not 

 only when the installations were on the same ship, but also 

 when they were on different ships „ 



For comparison purposes „ the Dynamic Monitor utilized a 

 cathode ray tube „ This gave a direct reading of the figure 

 of merit after two preliminary calibration adjustment s 6 The 

 procedure was a substitution method by which the measured figure 

 of merit was independent of the calibration of the electronic 



85 



