372 HAYES— U. S. NAVY MV TYPE OF HYDROPHONE. 



6. By giving a fairly accurate, intermittent sounding record while 



the vessel is under way in water of any depth, providing the 

 vessel is equipped with a suitable submarine sound-signaling 

 device. 



7. By giving the distance of a submarine sound signal. 



8. By locating icebergs, derelicts, or precipitous coasts at ranges 



sufficient for avoiding collisions. 



Hydrophones Developed by the U. S. Navy.^ 



The hydrophones developed by the United States Navy differ 

 from all others in that they employ a multiplicity of non-resonant, 

 underwater sound receivers, having sufficient time lag (compensa- 

 tion) introduced into the path of energy traverse between each re- 

 ceiver and the ear to bring the energy from all the receivers to the 

 ears in phase. 



The receivers are placed at equal intervals along a horizontal 

 line. The dimensions of the group of receivers (length of line) is 

 sufficiently great to cause an appreciable change in phase relations 

 between the responses from the several receivers whenever the 

 direction of the sound-source relative to the line of receivers is 

 changed. 



Navy hydrophones employing multiple receivers are of two 

 classes, namely ; those employing fixed compensation wherein the 

 line of receivers can be rotated about a vertical axis, and those em- 

 ploying variable compensation wherein the receivers are fixed in 

 position. The present paper deals with the latter class of hydro- 

 phones, the so-called " MV Types." 



Why the Navy Tested the Ability of the MV Hydrophone 



TO Safeguard Navigation. 



At the time of the Armistice the MV type of hydrophone, 

 although not completely developed, was proving to be superior to 

 other types of on-board installations. Accordingly when the prob- 



1 For a more complete description of various types of hydrophones, see 

 paper " Detection of Submarines," by Dr. H. C. Hayes, Proceedings of Amer- 

 ican Philosophical Society, Vol. XIX., No. i, 1920. 



