RADIO ACOUSTIC RANGING—ADAMS 225 
One minute before an R. A. R. position is desired, an electric bell 
signals the bomber to get a bomb ready. The bell signal also indicates 
the size of bomb wanted. A detonator and fuse are inserted in the bomb 
and the fuse is lighted a few seconds before the time for the position. 
When the fuse is burning, the bomb is thrown overboard from the 
ship’s quarter and a bell is rung as it strikes the water. This is the 
official time of the position. (The time of the explosion, which comes 
7 or 8 seconds later, is not the time of the position, because by that 
time the ship is some little distance away from the place of the explo- 
sion.) The electric bell is heard by the officer in charge and by the 
chronograph attendant. The time and log are read and recorded and 
a sounding is taken. Any changes in course or speed are made at this 
time. At the sound of the bell, the chronograph attendant starts the 
chronograph and connects it with the ship’s hydrophone. When the 
bomb explodes, the sound is received through the hydrophone and reg- 
isters automatically on the chronograph tape. After the explosion has 
registered on the chronograph tape, the chronograph is switched from 
the hydrophone to the ship’s radio receiver. The sound of the bomb 
explosion travels through the water in every direction and eventually 
reaches the several receiving stations. At the instant the sound arrives 
at each receiving station hydrophone, the radio transmitter connected 
to it automatically sends a radio signal, which is received on the ship’s 
radio receiver and registers on the chronograph. During this time, 
which may be from a few seconds to more than 100 seconds, a mark is 
being made each second (or each tenth second) on the chronograph 
tape. As the radio returns are registered, the chronograph attendant 
identifies them, and when the last one has been received, the time 
intervals, in seconds and hundredths of seconds, from the explosion to 
its receipt at the several receiving stations are taken from the tape. 
Each radio return and its corresponding distance must be correctly 
identified with reference to the station from which it was received. 
The time intervals are then reported by the chronograph attendant to 
the officer in charge who determines from them the position of the sur- 
vey ship at the time the bomb struck the water. This entire operation 
takes on the average about 4 or 5 minutes. 
R. A. R. RECEIVING STATIONS 
Three different types of receiving stations have been used by the 
Coast and Geodetic Survey. In their chronological development they 
are: Shore station, ship station, and sono-radio buoy. Ship stations 
are no longer used; shore stations are sometimes used; but sono-radio 
buoys are used in most R. A. R. surveys. 
Shore stations.—R. A. R. was first used by the Coast and Geodetic 
Survey on the Pacific coast of the United States. Here comparatively 
