RADIO ACOUSTIC RANGING (R. A. R.) 
By ComMMANDER K. T. ADAMS 
United States Coast and Geodetic Survey 
[With 1 plate] 
Hydrographic surveying consists essentially in measuring water 
depths from a survey vessel and locating those depths in geographic 
position or with reference to the adjacent land features. The method 
almost universally used for fixing hydrographic surveys within sight 
of land is by measuring two sextant angles to three appropriately 
located visible control stations. This is the well-known three-point 
problem. In hydrographic surveying such a position determination 
is called a three-point fix. The method is sometimes used beyond sight 
of land, where the depths of the water permit, by utilizing systems of 
anchored buoys for control stations. 
Beyond the limit of visibility of shore objects and where buoys can- 
not be used, hydrographic surveys were formerly controlled either 
by dead reckoning or by celestial observations. At considerable dis- 
tances from the coast and in deep oceanic areas, such methods sufficed, 
even though both are notably inaccurate as compared with the three- 
point fix method. However, there was serious need for a more accurate 
method for use in coastal waters just beyond the range of the three- 
point fix method. Radio acoustic ranging (R. A. R.) was developed 
for use in such areas. 
HISTORY OF R. A. R. 
Subaqueous sound was first used in navigation to determine the 
direction of an underwater sound source by means of two hydrophones 
(subaqueous sound receivers) installed on a ship, one on each side near 
the ship’s bow. A patent was granted for this device in 1894. Prob- 
ably the first practical use of subaqueous sound to determine hori- 
zontal distances at sea was by means of a submarine bell suspended 
below a lightship. Such bells were in general use by the United 
States Lighthouse Service in 1906. Other experiments were made in 
connection with the use of subaqueous sound in navigation, but the 
rapid development of radio direction finding fulfilled the need for 
position determination in navigation. The sinking of the Titanic in 
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