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a brief history of active sonar 71 Another major development in active echo-ranging systems occurred when the US Naval Research Laboratory developed the first ‘QA’ sonar, which was to become the first destroyer-mounted, echo-ranging sonar in the US Navy, operating at 15 to 20kHz. By 1933, the QA sonar was installed on eight destroyers. Subsequent improvements in transducer technology yielded the QC series, which was installed as a standard ASW active sonar on all US destroyers at the outbreak of WWII. 8 When two letter designators were used for US Navy equipment, the first letter indicated the type of equipment (Q represented Sonar Echo Ranging Listening equipment) and the second letter indicated the subtype of the equipment. 9 Use of the word ‘sonar’ for these systems, defined as Sounding Navigation and Ranging, was coined in 1942 by FV Ted Hunt, director of the Harvard Underwater Sound Laboratory. 10 All of the WWII sonars had transducers consisting of a flat faced array of elements in spherical or tear shaped housings that were mechanically lowered below the hull and also mechanically trained (turned) in azimuth. A Naval Sonar Operator’s manual published just after WWII provides a diagram of the traditional sonar dome (Figure 1). Between the late 1940s and 1960, in response to improvements in submarine technology and the increased threat this represented, surface ship active sonars were developed for the US Navy. The major Cold War active sonar technology development was the advent of scanning sonar to compensate for faster submarine speeds and the need to switch rapidly from long-range to short-range detection of an attacking submarine. In scanning sonar, the transducer becomes an array of elements arranged in a vertically oriented cylinder. This permits omni-directional transmission and reception. Scanning sonar provides directional search capability via sending and receiving focused sound energy in multiple directions simultaneously with different ping intervals. Longer ping intervals allow longer-range detections, which are derived from the time it takes for the ping to reach a target and for the echo to return. 11 The QHBa series was the first scanning active sonar, and it operated at 28kHz. 12 Figures 2 and 3 show a cut-away of a scanning sonar and a diagram of the QCB system, respectively. The AN/SQS-4 sonar was proposed in 1948 as a 14kHz equivalent of the QH sonar. The AN/SQS-4 was first tested in 1951 and entered fleet service in 1954, primarily on surface ships and some submarines. System designators were originally called the Army-Navy Nomenclatures System (the prefix ‘AN’). There is a three letter and a number designator for the surface ship sonars. ‘SQS’ signifies ‘S’ – Surface ship, ‘Q’ – Sonar, and ‘S’ – Search. The number represents the series. 13 The detection range of these sonars was limited by their operating frequency, leading to the development of lower frequency active sonars to minimise attenuation loss and thus increase detection ranges. Later versions of the AN/SQS-4 reduced the typical operating mode to four variants: (1) 8kHz, (2) 10kHz, (3) 12kHz, and (4) the original 14kHz. 14 The next improvement in surface sonars was RDT (Rotational Directional Transmission), which permitted increased transmitted power by pulsing groups of
72 australian maritime issues 2009: spc-a annual Figure 2: Cut-away view of the first scanning sonar transducer (Bureau of Naval Personnel, 1953) Figure 3: Pictorial diagram of the QGB System (Bureau of Naval Personnel, 1953)
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