Radio acoustic ranging, occasionally written as "radio-acoustic ranging" and sometimes abbreviated RAR, was a method for determining a ship's precise location at sea by detonating an explosive charge underwater near the ship, detecting the arrival of the underwater sound waves at remote locations, and
celestial body, and the first non-visual means to provide precise positions. First employed operationally in 1924, radio acoustic ranging remained in use until 1944, when new radio navigation techniques developed during World War II
rendered it obsolete.
Technique
To fix their position using radio acoustic ranging, a ship's crew first ascertained the temperature and
true range multilateration to fix the ship's position.[1][2]
In deep waters, such as those that prevailed in the
United States East Coast, where shallower waters prevailed, sound had greater difficulty in reaching the coast, and the Coast and Geodetic Survey relied more heavily on anchored station ships, and later moored buoys, to support radio acoustic ranging.[1]
Chronographs recorded times to the hundredth of a second, and the crew of a ship using radio acoustic ranging could determine their ship's distance from the remote hydrophone stations to within 50 feet (15 meters), allowing them to plot their ship's position with great accuracy for the time. With sound waves traveling from the point of the explosion to the distant hydrophones at about 0.8 nautical miles per second (1.5 km/s), ships occasionally used radio acoustic ranging at distances of over 200 nautical miles (370 kilometres) between ship and hydrophone station, and distances of 75 to 100 nautical miles (139 to 185 km) were common.[2]
Development history
Precursors
Radio acoustic ranging had its origins in a growing understanding of underwater acoustics and their practical application during the early decades of the 20th century, and developed in parallel with
lightvessels, and on buoys along the coasts of North America and Europe, and receiving hydrophones were mounted aboard hundreds of ships. It was history's first practical use of acoustics in an ocean environment.[1]
The
sinking of RMS Titanic in 1912 due to a collision with an iceberg spurred the Canadian inventor Reginald Fessenden (1866–1932) to begin work on a long-distance underwater sound transmission and reception system that could detect hazards in the path of a ship. This led to the invention of the Fessenden oscillator, an electro-acoustic transducer which by 1914 had a proven ability to transmit and receive sound at a distance of 31 nautical miles (57 km; 36 mi) across Massachusetts Bay and to detect an iceberg ahead of a ship at a range of 2 nautical miles (3.7 km; 2.3 mi) by bouncing sound off it and detecting the echo, as well as an occasional ability to detect the reflection of sound off the ocean bottom. Further impetus to developing practical applications of underwater acoustics came from World War I, which prompted the Royal Navy, United States Navy, and United States Army Coast Artillery Corps to experiment with sound as a means of detecting submerged submarines. In postwar experiments, the Coast Artillery Corps's Subaqueous Sound Ranging Section conducted experiments in shallow water in Vineyard Sound off Massachusetts in which it detonated explosive charges underwater at the ends of established baselines and measured the amount of time it took for the sound to arrive at hydrophones at the other ends of the baselines in order to establish very accurate measurements of the speed of sound through water.[1] And in 1923, the Submarine Signal Company improved upon its underwater signaling devices by equipping them with radio transmitters that sent signals both to identify the particular device and to indicate to approaching ships that it would generate an acoustic signal at a specific time interval after it sent the radio signal, allowing ships to identify the specific navigational aid they were approaching and to take advantage of a one-way ranging capability that let their crews determine their direction and distance from the navigational aid.[3]