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Figure 1. Acoustical Society of America (ASA) Pioneers of Underwa- ter Acoustics Medal.
to steer the ship toward a bell (Fay, 1912; Reynhout, 2002; Howarth, 2015). He is credited with leadership in underwa- ter acoustics over almost 50 years.
Reginald Fessenden joined SSC as a consultant a few months after the April 1912 loss of the Titanic (Fessenden, 1940). At SSC, he began development of active sonar with a device called the Fessenden oscillator (Fessenden, 1916, 1940; Seitz, 1999; Howarth, 2015). Although a transducer and not an oscillator, it utilized a vibrating faceplate exposed on one side to seawater and driven by a voltage applied to an electromagnetic coil that moved in an induced magnetic field (much like a modern loudspeaker). This created under- water acoustic signals in the form of tone bursts, and it also received echoes. Sea trials began in 1914, demonstrating underwater communications and iceberg detection. Experi- ments on submarine detection were done in 1917, and the US Navy began installing Fessenden oscillators for commu- nication on new submarines in 1918. Commercial “Fessen- den fathometers” came into use in 1924.
The pioneering electronic efforts of George Washington Pierce greatly supported advances in underwater acous- tics. Pierce served at the Naval Experimental Station in New London, CT, during WWI and developed sonar circuitry, including phase-delay “compensators,” to enable a binau- ral listener to determine the bearing of a signal from two or more external sensors on one’s own ship. He later capitalized on vacuum tube technology and developed many profitable
ideas, including the famous Pierce oscillator, which remains significant to this day. He was also a pioneer in magnetostric- tive transducers. These devices utilize the sound-generating expansion and contraction of certain metals when exposed to alternating electromagnetic fields, a process that also per- mits signal reception (Pestorius and Blackstock, 2015).
The early 20th century was a time of great advances in the physical sciences, including the development of relativity and revolutionary discoveries in atomic physics. The great French physicist Paul Langevin was at the center of these exciting developments. His professor (Pierre Curie) had codiscovered piezoelectricity, which is the ability of certain crystals, such as quartz, to expand and contract in an elec- tric field and to generate an electric charge when acoustically excited. WWI motivated Langevin to utilize this effect to de- velop ultrasonic sonar. Quartz crystals, mass loaded on both sides to lower their resonance frequencies, were used to de- velop high-resolution, narrow-beam sonars. The war ended before they saw service, but Langevin was able to demon- strate ultrasonic echo ranging for submarine detection and depth finding (Centre National de la Researche Scientifique [C.N.R.S.], 1950; Zimmerman, 2002; Sabra, 2015).
Harvey Hayes was the first Director of the US Navy Tor- pedo Station in New London, CT, during WWI. He became the first Superintendent of the Acoustics Division of the Naval Research Laboratory (NRL) in Washington, DC, on its founding in 1923. For the next 25 years, he supervised a huge variety of benchmark research projects, establishing this organization as a world leader in underwater sound. This successful laboratory became a model for the devel- opment of subsequent underwater acoustics laboratories worldwide, and more will be said about it below. Hayes was also the first recipient of the ASA Pioneers in Underwater Acoustics Medal in 1959 (Erskine, 2013, 2015).
WWI
The onset of WWI saw the allies ill-prepared for antisub- marine warfare (ASW), and only easily developed, primitive systems were fielded. Examples include the use of Thomas Edison’s carbon-granule microphone in a waterproof de- sign, which was deployed on a vertical column and used by British fishing boats in the war effort (Lasky, 1977; Figure 2). The resulting hydrophone was baffled against backward excitation, and its “cardioid” directivity was used to roughly sense a target’s presence and direction against noise. This device gave way to another quick solution consisting of a simple binaural pneumatic system. It utilized rubber bulbs
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