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meansaYS the U' S' Nayy's Principal Subrnari °f detecting and targeting face w "uS- Essentially- all Navy surfed Wj|^S *PS and submarines are fit- erjjpio SOnars’ antisubmarine aircraft some L exPent^at>le sonobuoys, and fars- W helicopters use dipping so- rnanV sea mines have sonars,
sukm flrst Soviet post-World War large?ar,'nes bega
ThenUmbers-
ar be^S'2y Passive/active mode °nWard yarne operational from 1958
while mi —
sonars countermeasure forces use
States m m'nes’ and the United soUnc| rTla es extensive use of seafloor These sSUrVeillance systems (SOSUS). Plough °nars 3re Pass‘ve or active—al- °Perati SOrne ecluipment is capable of S„,£‘" '»,h -ode,, trabiy j Sf"P sonars vary consid- Princjp^ ,fyPe and installation. The lJ. 5 ^ uU-mounted sonars in the 26/53 str|lVy t<)day are t,le SQS-23, SQS- hatj tbe'leS’ and sQS-56. These sonars When fLr orig'ns in the early 1950s,
Ij tlrci- ?an going to sea in
s°tl;
destr0yers rn°ciernized war-built FRAM ^h-93]) ! ^dernized Forrest Sherman (niaSS destroyers, and the new ^Dg-2) ,G-9> anci Charles F. Adams
titles w*" aSSes' initially, the sonar trad/6 btted under the hull, in d°WeVer tl0nal position of sonars. ’ °ne Forrest Sherman, the
e*
Barry (DD-933), and the last five Charles F. Adams-class ships (DDGs-20 to -24) have bow-mounted SQS-23 domes. Moving the sonar forward to the bow has the advantage of placing the sonar as far as possible from own- ship machinery and propeller noises. But it is not without cost. The SQS-23 bow sonar weighs 28 tons and has an internal volume of 8,000 cubic feet, resulting in a ship several hundred tons heavier than a non-bow sonar ship. The bow sonar also necessitates special care in maneuvering with tugs or pulling alongside a pier, and in docking the ship.
An even larger sonar, with perhaps double the 36-kilowatt power of the SQS-23, was sought by the late 1950s, as it became evident that the Soviets would continue to improve their submarines, especially with the advent of nuclear propulsion. In 1958, the Navy awarded contracts for competitive models of the larger and more-capable SQS-26.
In the early 1960s, the SQS-26 became the standard ASW ship sonar. Significantly, delays in delivery and technical problems caused the SQS-26 not to be approved for service use until November 1968. By that time, more than a score of ships had been fitted with the sonar: the Bronstein (DE-1037), Garcia (DE-1040), Brooke (DEG-1), and Belknap (DLG-26) classes and the Truxtun (DLGN-35). The sonars were of limited effectiveness during this period while the ships' long-range ASW weapon delivery capability was nil because of the short range of ASROC and the short-lived ASW helicopter (DASH) program.
The SQS-23 was no longer produced, and the larger SQS-26 went into the subsequent 46 ships of the Knox (DE- 1052) class and the two nuclear cruisers of the California (DLGN-36) class. A number of improvements were made to the SQS-26. A major advance was made with a shift to solid-state electronics, resulting in the new designation SQS-53. This sonar went into the Spruance (DD-963)-class ASW destroyers and the class variations, the Kidd (DDG-993) and Ticonderoga (CG-47) designs, as well at the Virginia-class, nuclear cruisers (CGN-38 to -41).
However, the SQS-53 was not provided in the latest ASW frigates of the Oliver Flazard Perry (FFG-7) class. The severe cost and size constraints imposed by the Chief of Naval Operations when they were designed led to the small, higher-frequency and thus shorter-range SQS-56 being developed for this large class. This sonar was developed from the SQS-36/38 hull-
l'm °f Symbols
Jo:
Installation
Snati
•on
A = aircraft B underwater (submarine) S = surface ship
Type of equipment
Q = sonar
G = fire control 26th series
N = navigation Q = multiple or special
R = receiving (passive)
S = search (active/passive)
Modification
AX
119
LITTON
7he solid-state SQS-53 sonar—pictured here without transducers—is the U. S. Nary's primary how-mounted sonar. It has proved to he particularly effective in its passive mode.
mounted sonars used in the Coast Guard’s Hamilton (WHEC-715) cutters. Use of the SQS-56 saved perhaps 600 tons of displacement in the FFG-7S, while requiring far less electrical power than the SQS-53’s 66 kilowatts. Other factors in deciding to reduce the Oliver Hazard Perry-class hull-mounted sonar effectiveness were the availability of large numbers of AN/SQS-26/53 sonars in other ASW ships and the potential of towed array sonars.
During the 1950s, the U. S. Navy developed two additional types of surface ship sonars: variable depth sonar (VDS) and towed array sonar (TAS). The VDS is lowered over the stern of the ship to place the sonar dome below the near-surface thermal layers that reflect sonar beams.
The principal U. S. Navy ships now using VDS are the Kwox-class frigates. They can use either their hull- mounted AN/SQS-26 or the AN/SQS-35 VDS, or radiate a sonar beam on one and receive its echo on the other. The VDS “fish” can be towed at relatively high speeds, and can be operated down to depths of several hundred feet. It is mechanically retracted and stowed on a cradle within the stern of the ship.
120
But the towed arrays have been more successful and are planned for much wider use in the fleet. The tactical towed array sonars (TACTAS) now in use in the Knox-c\ass frigates consist of a passive (hydrophone) system in a cable towed behind the ship. In the Knox class, the current AN/SQR-18A TACTAS is attached to the VDS towing body to facilitate handling.
By using convergence zone detection techniques, TACTAS has long- range capabilities against Soviet submarines, especially when employed by screening ships away from the noisy task force center. The AN/SQR-18A TACTAS, however, can be used at only slow speeds (although the array can be towed or reeled in or out while the ship is at higher speeds). The improved AN/SQR-19 TACTAS, which has encountered delays because of contractual and technical difficulties, is planned for installation in the 1980s in the Spruance and Oliver Hazard Perry classes, and possibly the Ticonderoga class. However, since the Aegis cruisers will operate in the center of the carrier task forces, often in close proximity to other ships, effectiveness of TACTAS may be questionable in these hulls.
A final surface ship sonar "type” is the surveillance towed array system (SURTASS) that is planned for the tug- type T-AGOS surveillance ships. These will provide long-range detection in areas where SOSUS is unavailable or limited.* The SURTASS/T-AGOS system will have the means of providing tactical data to warships but their primary purpose will be to transmit data via satellites to processing stations ashore.
While, surface ships rely heavily on active as well as passive sonar, the U. S. Navy tends generally to emphasize the passive sonar. This is especially true for submarines and the seafloor SOSUS complex. Fundamentally, passive sonars seek to detect the sounds radiated by a submarine—the signal—in a background of undesired sound—the noise. The key principle of passive sonar is the relationship be-
*See Norman Polmar, "SURTASS and T-AGOS,” March 1980 Proceedings, 122-124.
tween the signal and the noise, n° mally expressed as the signal-to-f ratio (SNR).
As submarines become quieter
signal has gone down. At
the
the same
time, the increases in ocean shipP11^ and offshore oil drilling have the background noise. Thus, rnuC the current effort in sonar techno
seeks to counter this decreasing
SNR'
The noise produced by submarine^ both narrowband and broadband- ^ ciprocating and rotating machine' generate the narrowband errn For a submarine with alternating
issi°nS'
cur-
icies
rent electrical systems, the freqoen and amplitude of many of these sions are independent of the .
ern>s‘ p's
soon*
of *aff 0f fluid*
speed. Broadband spectrum can be caused by the flow over the hull, the turbulence in internal piping (such as steam ^ nuclear plant), and mechanica
friction. Propeller noises are narro^ and broadband, with the soun ^s, to cavitation, when it °c dominating the broadband spec
• sov*et
Several actions are possible to ^ submarine designers to reduce passive “signatures,” in turn caU |
the American scientific-tec ^ community to work harder °n^jVC
SNR. Of course, in wartime, PaS,
■d by the
sonar operation could be frustrate the extensive use of noisemaketS’
and v’
use of weapons in the ocean, submarine tactics. In particular. seems vulnerable to a number o
and passive countermeasures. ■
publications indicate that SOSUS tions are well known.
Active sonars are less vU*n ,Nig to the .of
than passive sonars are
. so:
iSfl5
the
abdky
problem but have the vulneran- —^ announcing the presence of the s ing surface ship or submarin^et helicopter with dipping sonar)- ^ submarines are known to use anechoic coatings to reduce the tiveness of active sonar. . \,e-
Thus, there is a see-saw batt tween improvements in sona^je thc dally improving the SNR, w slJb'
re'
.flee-
Soviets are developing qu'fter marines and employing tactics duce their vulnerability to detec
to
(To be continued in
the A"SHS"SS'“
Proceeding3
/juiy
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