44 HAYES— DETECTION OF SUBMARINES. 



tain advantages over the acoustical. It is more sensitive and there- 

 fore capable of giving greater range. It can be housed within a 

 water-tight blister in such a way that the line of receivers can be 

 withdrawn through a hand-hole opening in the skin of the ship and 

 repaired or replaced without docking the boat. The installation as 

 a whole has proved more durable than the acoustical lines. If a re- 

 ceiver becomes defective it can be cut out and the line can still be 

 used, whereas a leak in the acoustical line allows the installation to 

 fill with water and thus become useless. Finally, the compensator 

 can be placed on or near the bridge whereas the listening station for 

 an acoustical MV must be placed near the inlets through the ship's 

 skin. This location must necessarily be near the keel of the boat and 

 as a result considerable distance from the bridge. 



On the other hand, the quality of the sound and the selectivity 

 given by the acoustical MV is superior to that given by any electrical 

 MV thus far produced because of the fact that the acoustical re- 

 ceivers are better matched than are the microphone receivers. How- 

 ever, improvements in the construction and matching of the micro- 

 phonic receivers are continually being made and there is all reason 

 for believing that the electrical MV will soon be made to compare 

 very favorably with the acoustical MV as regards quality of sound 

 and selectivity. 



The perfection of the electrical MV has made possible the use of 

 two or more lines of receivers with the same compensator. The type 

 AE-2 electrical compensator developed for use with the multiple 

 microphone eels is provided with a multiple unit switch whereby it 

 can be connected with either the two eels, as described, or to two 

 " on-board " lines enclosed in blisters. This combination is very 

 favorable for searching submarines for the reason that the eels can 

 be used for picking up faint or distant sounds thereby directing the 

 listening boat to a point where the submarine can be heard and fol- 

 lowed by means of the " on-board " lines. Moreover, the distance of 

 the submarine can be judged with some accuracy by determining its 

 bearing on both the eels and the " on-board " lines. The distance 

 between the eels and the blisters being known the range of the sub- 

 marine is readily determined by triangulation. While this method 

 does not determine range with sufficient accuracy for bombing pur- 



