axis so that a single signal will have multiple arrival times with a signature of multiple pulses climaxing in a sharply defined end. That sharply defined end representing a near axial arrival path is sometimes termed the SOFAR finale and the earlier ones the SOFAR symphony. Those effects are due to the larger sound channel in which ray paths are contained between the surface and critical depth. Critical depth is the point below the sound speed minimum axis where sound speed increases to equal the maximum speed above the axis. Where bottom lies above critical depth the sound is attenuated, as is any ray path intersecting surface or bottom. The channel axis varies most with its location reaching the surface and disappearing at high latitudes (above about 60°N or below 60°S) but with sound then traveling in a surface duct. A 1980 report by Naval Ocean Systems Center gives examples in a study of a great circle acoustic path between Perth, Australia and Bermuda with data at eight locations along the path. At both Perth and Bermuda the sound channel axis occurs at a depth of around . Where the path meets the Antarctic convergence at 52º south there is no deep sound channel but a in depth surface duct and a shallow sound channel at . As the path turns northward, a station at 43º south, 16º east showed the profile reverting to the SOFAR type at . Applications The first practical application began development during World War II when the United States Navy began experimenting and implementing the capability to locate the explosion of a SOFAR bomb used as a distress signal by downed pilots. The difference in arrival times of the source at an unknown location at known locations allowed computation of the source's general location. The arrival times form hyperbolic lines of position similar to LORAN. The reverse, detection of timed signals from known shore positions at an unknown point, allowed calculation of the position at that point. That technique was given the name of SOFAR backwards: RAFOS. RAFOS is defined in the 1962 edition of The American Practical Navigator among the hyperbolic navigation systems. The early applications relied on fixed shore stations, often termed SOFAR stations. Several became acoustic research facilities as did the Bermuda SOFAR Station which was involved in the Perth to Bermuda experiment. The records of the Bermuda station are maintained by