Page 44 - 2016Fall

History of Underwater Sound
at each end of a steerable vertical column, with sonic tubes brought into the submarine or ship to a stethoscope, en- abling a trained operator to scan the horizontal azimuth for noise radiating targets in the 500- to 1,500-Hz band (Klein, 1968). Passive listening systems such as these were the main systems deployed by the allies. Sonar research by Langevin and others was successful but did not produce fleet systems before the war’s end.
Several turning-point events in underwater acoustics re- search were initiated during WWI. The US Navy had largely depended on SSC up until the United States entered the war in 1917, and this quickly changed with the establishment of the Naval Experimental Station in New London, CT, for technology development (Lasky, 1977). This marks a trend toward creation and reliance on in-house Navy laboratories for independent research, development, and advice inde- pendent of the profit motive.
Figure 3. A. B. Wood.
acoustics, doing groundbreak- ing research, serving as Deputy Superintendent of the Admi- ralty Research Laboratory, and writing a classic acoustics book (Buckingham, 2015). He was awarded the ASA Pioneers of Underwater Acoustics Medal in 1961. A medal of the (Brit- ish) Institute of Acoustics for achievements by young re-
searchers is named in his
Figure 2. World War I carbon button and pneumatic hydrophones.
British involvement in WWI was much larger than that of the United States. A young Albert Beaumont Wood (Fig- ure 3) had come into underwater acoustics in 1915. He and Robert W. Boyle worked with Langevin in France but devel- oped their own piezoquartz transducer ideas for their early sonars, which were called “asdics” in the United Kingdom, a code word meaning “antisubmarine-division-ics,” with the “ics” at the end as in physics. At the start of WWII, Wood was awarded the Order of the British Empire in recogni- tion of his work on dismantling an enemy magnetic mine. A. B. Wood became an international figure in underwater
honor and is given to North Americans in alternate years. His professional achievements and interesting accounts of his own war experiences are doc- umented in the Journal of the Royal Naval Scientific Service
(Wood, 1965).
Post-WWI Efforts
After WWI, many American, British, and French scientists and engineers were busy developing the ideas born during the conflict. The first research efforts involved transduction. It was shown that Langevin’s transducers could be made to work as highly directional echo-ranging devices. G. W. Pierce developed magnetostrictive transduction for depth sounding. US transducer efforts also focused on piezoelec- tric crystals of Rochelle salt. The NRL extended these tech- nologies to submarine detection and developed an electro- acoustic system for binaural listening (Klein, 1968).
This era saw industrial concerns develop an inventory of “searchlight sonars” for both surface ship and submarine use (Figure 4). The US sonars operated at frequencies of 24-30 kHz, above the frequency range of human hearing, which reduced intercept detection. They were also above the fre- quencies of most shipboard machinery noise sources as well as above the range of most wind driven sea-surface noise. These sonars worked by transmitting a short tone burst or “ping,” typically 20-200 ms long, within a fairly directive “conical” beam, typically around 10° wide at the half-power points. Echoes were received from targets before the next ping was transmitted (National Defense Research Commit- tee [NDRC], 1946a).
An important hydroacoustic problem was solved in 1937 by Elias Klein and others at the NRL who determined that the blunt edges on propellers led to cavitation, excited reso- nances in the propellers, and caused noisy vibrations aboard
42 | Acoustics Today | Fall 2016