were functioning far below their expected efficiency,, Disturbed 

 at this news, the Navy requested HUSL to investigate the prob- 

 lem further on a "local aid" basis « 



The findings on DAHLGREN and ITIELDS aroused doubt concern- 

 ing the acoustical oerformance of dome installations at a time 

 when the Navy had begun to install streamlined domes on all 

 escort vessels so that sonar equipment might be used at higher 

 speeds. A program of measurement was laid out to determine 

 whether the two defective installations were typical., 



In all, seventy installations on as many ships were testedo 

 The Harvard scientists were shocked to discover that in many 

 cases the intensity of the sound being transmitted into the 

 water was so low as to render the echo-ranging equipment virtu- 

 ally useless o Equipment with unpainted domes was found to have 

 considerably better patterns than those with painted domes. 

 Yet even the patterns of gear with unpainted domes were still 

 inferior to those of equipment at test stations. It became 

 apparent that the anti-foul ing painting 9 while an important 

 factor j, was not the only cause to which the deterioration of 

 projector patterns could be attributed. 



Tracking down the source of this poor performance , the 

 Harvard research workers made a discovery in tests on the 

 destroyers USS KENDRICK S USS LAUB and USS MACKENZIE, all of 

 which had been equipped with unpainted domes. When tests 

 made with the Sound Gear Monitor showed that these domes 

 were seriously impairing the performance of the sonar gear, 

 the domes were replaced by new corrugated models which had 

 been found to be superior to the older domes. But the meas- 

 urements taken after the installation of the corrugated domes 

 revealed that the sonar equipment had suddenly become almost , 

 wholly inoperative, Despite the fact that the electrical per- 

 formance was excellent, acoustically both the transmitting 

 and receiving responses were found to be at least 20 decibels 

 or ten-fold below reasonable expectations, 



This was bad news to those responsible for the imminent 

 sailing of these vessels for convoy escort duty. During the 

 heightened activity which followed the discovery, study of 

 the evidence suggested that some feature of the commercial 

 anti-freeze solution used to fill the dome was the cause of 

 the failure, A laboratory experiment was quickly arranged 

 which showed that when the transducer was dipped in the anti- 

 freeze solution it collected a thin wax-like deposit which 

 caused a sharp drop in its response. On the basis of this 



