AN/SQS-35 and AN/SQR-18A

History

AN/SQS-35 is a large towed array active sonar housed in a composite "fish". AN/SQR-18/18A/19 is a towed hydrophone array known as TACTAS.

From World Naval Weapons Systems:

  The interim escort towed-array surveillance system (IETASS) was developed under the escort towed-array sensor (ETAS) program. SQR-18 was conceived as a simpler alternative to SQR-14/15. Work began under the FY68 program. One Patterson experimental array (PEA) was bought in FY72, leading to a specific operational requirement in FY73. IETASS was tested on board Knox-class frigates and a minesweeper, leading to the ETAS (program established FY75) and then to the TACTASS (tactical towed-array sonar) programs. Contracts for 2 IETASSs were awarded in August 1974. In FY80, 12 were retrofitted to Knox-class frigates, 4 more following in FY81.
  The original SQR-18 was towed at depths of up to 366m, at the end of a 1706-m cable. SQR-18A was the original production version, towed from an SQS-35 fish at the end of a 1524-m cable. SQR-18A(V)1 is an improved version deployed on board Knox-class frigates, towed from their SQS-35 VDS fishes on a 730-m cable. A modified version, SQR-18A(V)2, which does not require a sonar fish, uses a special depressor and a 5300-ft cable. -18A(V)2 [sic] is towed by those Knox-class frigates that were never fitted with VDSs and by some Perry-class frigates. SQR-18(V)2 uses the same array-handling system, OK-410, as does SQR-19. The array itself consists of 32 vibration-isolated hydrophones (8 modular hydrophone sections), with preamplifiers in the fish; it is 730ft long and 3.25 in in diameter. SQR-18 is towed at depths of up to 366m on a 1706-m cable.
  SQR-18A(V)2 can use an EDO-developed short-scope tow, an alternative to a critical-angle tow requiring much less towing cable. The longer critical-angle tow is generally needed to isolate the noise of the towing ship from the array. However, EDO developed an own-ship noise canceler that can subtract the measured self-noise of the towing ship from the output of the array. The array is held down by a special depressor, a low-drag winged body with a V-tail and trailing-edge flaps on the tail fins, weighting 256 lb. The array passes through the depressor shell, for easy handling. This device was tested at sea in July 1981 on board the research vessel Athena, a former fast motor gunboat, at up to 34 kt, and then on board the surface-effect craft JEFF-A in August 1981 (at over 40 kt).
  Late in 1981 the upgraded SQR-18A entered service. The 800-ft array consists of an 8-module acoustic aperture, vibration-isolation modules, a tow cable, and a rope drogue. The upgraded version enjoys better flow-noise damping, is more rugged, and suffers from less self-noise. Given the modular design of the array, 1 section can be replaced if it fails (a ship can carry spare modules); formerly, the entire array had to be replaced. SQR-18As have been fitted with EDO's ALICE (adaptive line canceler and enhancer), consisting of an SQR-18A embedded post-beam-former interference canceler (EPIC) and an SQR-17 adaptive line enhancer (ALE). EPIC cancels a companion ship's sound so that submarines can be detected when a towed-array ship is escorting a very noisy ship. The engineering-development model was completed in February 1982.
  SQR-18 entered service only 5 yr after initial demonstration and suffered from unreliability. Compared to the original SQR-18, SQR-18A, the production version, has a low-noise array, an interference canceller, and an improved tracker. Production began in 1978, and an improvement program began in April 1981. The Dutch (2) and Japanese (6) navies have bought this system. 
  Produced by EDO, and also now manufactured by Gould, SQR-18 was initially to have been replaced altogether by the superior SQR-19; but development continued as insurance against any problems in the -19 program, and the -18 is an alternative standard.
  SQR-18 was first tested on board USS Moinester in 1975; -18A was tested in 1978. The initial results were that -18 was effective (but unreliable) in the first CZ, and that -18A corrected the demonstrated deficiencies. Only 2 SQR-18s were built, virtually all arrays being SQR-18A.
  The newest projected version, SQR-18A(V)3, will use the EDO AMSP parallel processor.
  Unlike SQR-19, SQR-18A has never used a standard nomenclatured beam-former or processor. Instead it uses a 2-screen Diagnostic/Retrieval unit related to SQR-17. Inboard electronics consist of a signal conditioner, a digitizer, and a signal processor, for both narrow- and broad-band. SQR-18A can operate in both broad- and narrow-band simultaneously, tracking by means of an automatically stabilized tracker beam and automatic target-following circuits. All processed data are stored electronically; the system does not use LOFARgrams. Each display can show up to 4 LOFAR channels; the results of signal measurement (frequency and amplitude of tonals, harmonic ratio, and tag frequencies) are shown as alphanumerics. 

Description of AN/SQS-35 here: [1]

Description of AN/SQR-18A here: [2]

Comments

This was a difficult project due to lack of online resources. Apparently the AN/SQS-35 "fish" is related to the AN/SQA-13 system, so I used the dimensions of that, which were available. Photographs of a Knox-class frigate seem to confirm the size. All TACTAS arrays, AN/SQR-18, 18A(V)2, 18A(V)3 and 19 should look similar in SB scale but I cannot confirm this. The cradle is drawn from photographs rather than diagrams and should be roughly correct when compared to real USN and JMSDF equipment. Use this part with caution.

Charguizard (20/09/2023)

Used on

AN/SQS-35

• Knox-class

AN/SQR-18A/19

• Knox-class
• Oliver Hazard Perry-class
• Spruance-class

Part description

The component is drawn partially wrapped around so it would fit in a template. Note that you can have only the SQS-35 "Fish" on a ship without the TACTAS, but I do not know how the TACTAS is deployed by itself without a "fish". The tether cable would be about 1600m long when fully deployed, which is impractical for an SB drawing, so I chose to represent it The distance between the "fish" and the hydrophone is accurate, and so is the hydrophone's length. The end is capped by a small drogue which is hard to represent in scale, and of which I have no good photographs.