230 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
The hydrophone, through which the sound of the bomb explosion is 
received, is installed in a water-filled tank which is fastened to the 
inner side of the hull of the ship. It must be located where ship noises 
will affect it least. 
Any good commercial communication radio receiver may be used so 
long as it will cover the necessary range of frequencies. 
The chronograph amplifier is especially built by the ship’s radio 
technicians. Its purpose is to amplify the impulse from the hydro- 
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FicurE 2.—Ship equipment for radio acoustic ranging. A bomber (a) threws 
a small TNT bomb overboard from the moving survey ship. The sound wave 
produced by the subaqueous explosion travels (CCC) to a hydrophone (d) in 
the bottom of the ship. The hydrophone converts sound energy to electric 
energy, which is led (EEE) to an amplifier which operates a chronograph (f). 
The bomb explosion is registered on a paper tape at G. The sound wave of the 
explosion travels to R. A. R. stations which it actuates and which instantly 
send radio signals (HHH) which are received (JJJ) and amplified and regis- 
tered on the same chronograph (f). The returns from three stations are shown 
at K, L, and M. Knowing the velocity of sound in sea water, the time intervals 
on the tape can be converted into distances. 
phone caused by the bomb explosion and also the output of the radio 
receiver. The amplification must be sufficient to actuate the stylus in 
the chronograph. 
A chronograph is a graphic-recording time-measuring device. It is 
connected to a break-circuit chronometer, which provides the time 
record. A narrow wax-coated paper runs through the chronograph 
beneath two sharp styluses electromagnetically operated. The tape 
moves at the rate of about 2 centimeters a second. One stylus is con- 
