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



doubtless require submarine code signals to be sent out at frequent 

 intervals during conditions of low visibility. These signals will des- 

 ignate the code number or " call " of the ship, its compass course and 

 possibly the speed which it is making. Other vessels in the vicinity 

 on receiving these signals and on obtaining a hydrophone bearing 

 upon them will have at their disposal much valuable information 

 which will aid them in steering a clear course and avoiding disas- 

 trous collisions. 



Such bearings will be far more trustworthy than those afforded 

 by fog whistles now universally used, not only because of the greater 

 ranges at which they may be obtained but also due to the fact that 

 the sea is a relatively homogeneous and stationary medium which 

 permits the definite linear propagation of sound. Every navigator 

 knows the unreliable nature of fog whistles which are not only dead- 

 ened by a counter wind, thus giving an erroneous idea of range, but 

 which frequently suffer erratic and wholly indeterminate refractions 

 and reflections as they encounter fog banks and cross-currents of 

 air. As a result their propagation is far from linear so that false 

 bearings of their source are obtained from which dangerous emer- 

 gencies sometimes arise. 



Locating Icebergs, Derelicts, etc. 



Because of its focusing ability, the MV hydrophone can deter- 

 mine the direction of comparatively faint sounds while the vessel, 

 upon which it is installed, is underway. If the sounds come directly 

 from the source, it gives the bearing of the source ; but if the sound 

 has been reflected, it gives the bearing of the reflecting surface. 



Direct tests for locating icebergs and derelicts by hydrophone 

 have not been undertaken to date but indirect evidence obtained while 

 conducting tests at New London, Connecticut, leads strongly to the 

 belief that such obstructions can be located by hearing and determin- 

 ing the direction of submarine sounds reflected from their surface. 

 The writer has often located the piers of the railroad bridge at New 

 London, Connecticut, by the reflected propeller sounds of the listen- 

 ing vessel and has also been able to locate Valiant Rock, which lies 

 in the passage between Fishers and Little Gull Islands, and in a like 



