Page 48 - 2016Fall

History of Underwater Sound
The NRL missions in WWII were in solving a myriad of problems, including remedial engineering of existing sonar for tactical ASW applications in actual warfare. One of these was to redesign the soundhead tilt mechanism so that the fleet surface ship sonar could “look downward” at steep an- gles to maintain echo location on submarine targets. Appli- cation of research discoveries made elsewhere were reduced to naval practice and made available to the fleet. Unique de- vices involving countermeasures and weapons systems were also developed to overcome wartime problems (Lasky, 1977; Erskine, 2013).
NRL field assets were also established for research and test- ing. The Navy’s first acoustic test range was developed in Key West, FL, and the NRL’s Leo Treitel developed instrumen- tation to test the sonars of warships passing through a test track to test the proper operation of their sonar systems.
The David Taylor Model Basin (DTMB) was named after Rear Admiral David W. Taylor, who constructed the first US facility for hydrodynamics research on ships at the Wash- ington Naval Yard in 1898 and was a world-renowned naval architect. The DTMB facility was built in 1939 and today is part of the Naval Surface Weapons Center Division at Card- erock, MD. Although largely a hydrodynamic research facil- ity, the DTMB has been a center for underwater acoustics because there is a strong relationship between hydrody- namic flow and self as well as radiated ship signature noise, which is detected by passive (listening) sonar.
In the early days of WWII, a young physicist named Mur- ray Strasberg (Figure 11) joined a DTMB group involved in submarine noise problems, headed by William Sette. They made measurements on cavitation noise bubbles gener- ated by model propellers in the DTMB water tunnels and studied the inception of cavitation bubbles as a function of ambient pressure. Strasberg was the first to notice that the onset of cavitation noise occurred before it could be visu- ally observed and identified an additional noise-generating cavitation effect originating from the propeller tips (NDRC, 1946b). He made the first sea trials on three Guppy class (SS 212) submarines, measuring propeller cavitation with spe- cially installed outboard hydrophones. He went on to de- velop new propeller design principles, which utilized differ- ent shapes and number of blades. Murray Strasberg was later to publish in The Journal of the Acoustical Society of America (Strasberg, 1956), and he became a key ASA leader, serving as president (1974-1975) and receiving the Gold Medal in 2000.2
Figure 11. Murray Strasberg and the propeller tip cavitation.
A number of organizations conducting WWII research with those mentioned above were quite active and were not de- scribed here due to space limitations. One of these was the MIT Underwater Sound Laboratory, which did work on un- derwater noisemakers used to confuse enemy weapons sys- tems (NDRC, 1946e). Perhaps the greatest MIT contributor to the war effort was Philip Morse. Vannevar Bush selected him to head the ASW Operations Research Group, which had the responsibility to guide the fleet on the effective use of their sonar, radar, and weapons systems to maximize their impact (NDRC, 1946f). His knowledge of physics and acoustics served him well in this endeavor. Morse went on to write acoustics textbooks, become president of the ASA (1951-1952), and receive its Gold Medal (1973).
Perspective
Some brief highlights of underwater acoustics in the eras sketched here have focused on noteworthy people, places, and examples of developments that were involved. Some truly sig- nificant features of ocean acoustics were discovered in these eras, for which we have only been able to give qualitative mention. Many of these efforts simply had to be done, mostly in times of war, but they became scientific and engineering achievements in their own right. Acousticians from all disci- plines were involved, whereas others from completely differ- ent disciplines were also engaged. It is interesting that many of the basic and applied research discoveries made in both WWI and WWII could not be utilized before the wars ended. These achievements have since been further explored and now ap- pear in modern texts as well as in the acoustics literature. The history of WWII shows the significant role underwater acous- tics played in its outcome, and much credit is due to those members of the ASA who contributed.
2 David Feit presented a paper, “Underwater Acoustics Research at the David Taylor Model Basin,” during a panel discussion at the special session “Historical Perspectives on the Origins of Underwa- ter Acoustics II” at the 169th meeting of the Acoustical Society of America held in Pittsburgh, PA, 2014.
46 | Acoustics Today | Fall 2016