CSU 90

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U32 of the type 212 A on overwater travel.

The Compact Sonar U-Boats 90 (CSU 90) is a composite of sonar systems developed by Atlas Elektronik that is used in five different classes of submarines . The overall system, designated by the Bundeswehr as DBQS-40FTC, consists of the medium-frequency Bugsonar DSQS-21DG together with the AN5039A1 Intercept-Sonar, the low-frequency flank antennas FAS 3-1, the PRS 3-15 for passive distance measurement, the FMS-52 ( MOA 3070) mine avoidance sonar and a tow sonar (TAS 83 or DTA 50).

overview

The target location by sonar always proceeds according to the same pattern: First, a contact is located on a broadband basis, i. H. the noise energy of the contact in a particular bearing is over all frequencies in a time interval integrated . This means that only the angle to the contact is known, which is recorded over time. The incoming noises are analyzed in a narrow band as soon as they are clear enough. First, the contact is subjected to a LOFAR analysis. LOFAR stands for LOw Frequency Analysis and Recording . The characteristic frequency lines of the contact are analyzed in order to classify the target (e.g. Broadsword class ) or even to identify it (e.g. HMS Battleaxe). The following DEMON analysis determines the speed of the target. DEMON stands for Demodulation Envelope Modulation On Noise , and converts the blade frequency into a rate of rotation and this into a driving speed. For this purpose, it must be known through military intelligence or espionage how many blades the propeller of the target vehicle has, but above all how fast the vehicle is traveling at a certain speed of rotation. The design of military ship propellers is therefore secret in order to make the DEMON analysis difficult or impossible for the opponent. In the last step, the Target Motion Analysis (TMA), the bearing angles are correlated over time with the speed vector of the ship. Ideally, there is only one solution so that the position, course and speed of the contact are now known.

The German submarine sonars are divided into four generations: The first generation were non-integrated passive systems, the group listening devices . The second generation CSU 3 used integrated sonars in which the antenna was connected directly to a console. The third generation was the standard Sonar 80 (ASO 80, CSU 83, DSQS-21, DBQS-21D) with a passive range finder (PRS) as a stand-alone , automatic spectral DEMON / LOFAR analysis based on SIP 3 and digital beam swiveling digital beamforming . In the latest, fourth generation, the standard Sonar 90 (DSQS-23, DBQS-21DG, CSU 90), all antennas and consoles are connected via a common fiber-optic bus, and the Target Motion Analysis (TMA) has now also been automated. The data is passed on to the combat system of the submarine. Except for the first batch of the 212 class that uses the MSI-90U, this is the ISUS 90 from Atlas Elektronik.

Various sources also report on the development of a new Sonar 2000 with the ISUS 2000 combat system based on COTS . Here, for the first time, LPI active sonar is to be used, which is difficult to locate by opponents due to its low-probability-of-intercept properties. Furthermore, new, planar side antennas (Improved Flank Array Sonar, IFAS) with 30 × 0.7 m are to be used. Use in class 216 submarines would be conceivable. The order of the 218SG class by the Singapore Navy , for which a tailor-made command and control system is to be developed by ST Electronics and Atlas Elektronik, could perhaps absorb these developments.

technology

Sonar systems

In the CSU 90, all antennas (bow cylinder, intercept sonar, side sonar, navigation sonar, PRS, towing antenna and noise monitor) feed on a common fiber optic bus which is connected to three consoles. The data from the CSU 90 are in turn fed directly into the ship's combat system. In the first batch of the 212 series, the Kongsberg MSI 90U mission control system is installed, later batches and boats ( 214 series , Dolphin class , Heroine class) use the ISUS 90 from Atlas Elektronik.

Bow sonar

Position of the bow sonar.

The DSQS-21DG is installed as a bug sonar. The cylindrical hydrophone assembly (CHA) is on top of the bow . The information published is practically zero. However, it should be an active / passive medium-frequency sonar in the frequency range from 0.3 to 12 kHz, which is unlikely to be broadband. The diameter of the cylinder base of the cylinder ring on which the transducers are mounted is also unknown. Other sources list the overall system DBQS-40FTC (CSU 90) as part of Sonar 90, without specifically addressing the bow sonar of the submarines.

Modern bow sonars usually have piezo-based sound transducers in polyvinyl fluoride , which, like active electronically scanned arrays, can form and swivel virtual signal lobes. 32 to 64 virtual signal lobes can be formed, which are stabilized against 25 ° rolling and 8 ° pounding by electronic beam swiveling. The antennas of the Sonar 90 family cover the frequency range from 2 to 11 kHz when the system is operated purely passively.

The cylinder sonars of the Sonar 90 can work simultaneously actively and passively. In active operation, a bandwidth of 1 kHz is used for purely passive reception. Two different CW frequencies can be used during a ping . Sending still takes place in the same way. The pulse length can be between 5, 50 or 300 ms. Either CW, FM or a combination of both can be sent, e.g. B. 50 ms CW followed by 50 ms FM. The received data from CW and FM are processed in parallel to achieve faster results. The CW component is used to calculate the Doppler effect in order to determine the radial speed of the target, the FM component profiles the target lengthways and thus outputs the course angle and body length of the target.

The intercept sonar receiver, which works in the frequency range from 1 to 100 kHz, can be retrofitted as an option. It uses both the bow sonar and a separate interception sonar antenna to locate medium and high frequency active sonars

Side sonar

The FAS-1 is integrated as a side sonar on the port and starboard side, which as part of the CSU 90 is given the designation FAS 3-1. The antennas should each be 20–48 m long and operate in the frequency range from 10 Hz to 2.5 kHz. Each antenna system consists of 192 hydrophones and covers an angular range of 90 ° with an accuracy of about 1 °. Although the flank array systems (FAS) have a linear transducer arrangement, according to the patent they can also determine the elevation angle to a noise source. The length of each antenna sausage is given here as 30 m, which corresponds well with the appearance . Since the bundling of these antennas in the vertical direction is very low or does not exist at all, only the apparent angle of incidence of sonar signals from other vehicles is measured, the apparent angles of incidence lying in one plane. This angle of incidence represents an apparent side bearing, which is composed of a true horizontal angle and a true vertical angle. By changing course and changing the trim position, i.e. tilting the submarine around its horizontal transverse axis, there is a changed apparent direction of incidence of the sound waves, and as its components also changed horizontal and vertical angles. The signal processing device can thus also calculate the elevation angle to an underwater vehicle through several measurements of the angle of incidence.

Navigation sonar

The FMS 52 is used as a mine avoidance and navigation sonar. The system is installed on the bow front. On Class 212 boats, it is over, and on Class 214 boats, under the torpedo tube mouths. It transmits in the frequency range of 30 kHz for mine search and 70 kHz for mine identification. The small phase-controlled antenna covers a range of 90 ° in elevation and azimuth, with a beam width of 3 °. Probably 32 virtual signal lobes can be generated. The system is used to locate anchor mines, rock formations in fjords or other obstacles.

Passive ranging system

Position of the PRS.

The Passive Ranging System 3 was adopted by the CSU 83 and consists of three antennas on each side. Antennas of the PRS 3-15 version are installed in the CSU 90. Each antenna consists of 15 lines and has a total of 60 hydrophones that receive in the frequency range from 2 to 8 kHz. Targets can be sighted in the range of 45 ° to 135 ° and 225 ° to 315 ° relative to the longitudinal axis with an accuracy of 0.5 °. The usable angular range is 170 ° on each side.

The PRS determines the distance to a noise source by the curvature of the wave front, which is determined by the time delay of the wave front on the antenna elements. Each curved wave front of incident sound waves reaches the three sensors with time differences that depend on the distance from the vehicle and the direction of incidence of the sound waves. The location of the vehicle is determined from the time differences determined by correlation. For this purpose, the bearing to the target is determined for each of the three antennas on each side by time-of-flight or phase compensation, and focus signals are formed whose focal points are lined up on the bearing beam to the target. The largest focus signal indicates the location of the target. The course and speed of the contact can be calculated automatically. The effective range is up to 15 kyd (13.6 km).

Towing sonar

The towing sonar is located at the rear end of the pressure hull and is rolled up on the top on a roll. The trailing cable is rolled in and out noiselessly using a patented process. In the 212 class boats, the cable runs diagonally from above in the stern of the submarine behind the pressure hull to a boom on the lower starboard side, where it enters the water in front of the X oars. This unfavorable construction was rectified in the boats of the 214 class: The oars are cross-shaped here, so that the lowest one also serves as the boom of the towing sonar.

According to older sources, the low-frequency, passive tow sonar is the TAS 83, which is the submarine version of the TAS 90 for surface ships. The towed antenna receives in the range 15 Hz to 1.2 kHz, possibly up to 2.4 kHz. However, newer sources speak of an antenna with a smaller diameter, so the TAS 83 on the 212 and 214 submarines has been replaced by a 50 mm thick antenna system DTA 50 (ref. Possibly TAS 3). The apparatus is 150 m long, with 20 m long vibration isolators at each end. Since the cable is 200 m long, the antenna is pulled about 210 meters behind the boat. The combination of side and trailing sonar enables the distance to be determined by triangulation. The maximum roll-out speed is 8 knots, the maximum hearing speed 12 kn, and the maximum driving speed 20 kn. The antenna can be rolled up again after use, but can also be cut in an emergency.

The change to a thinner 50 mm antenna became possible because sound transducers were manufactured as Macro Fiber Composite (MFC) for the first time. A layer of piezoceramic fibers is fixed between two intermediate layers of epoxy resin and the composite is covered at the top and bottom by a layer of polyimide on which a finger-like interlocking electrode pattern is printed, which runs at right angles to the piezoceramic fibers. These electroacoustic transducer patches are fixed on the outside on a series of hollow cylinder pieces that are connected to one another by electrical cables and are housed in a rubber tube like a pearl necklace (with a distance from “pearl” to “pearl”). Various patents from STN Atlas indicate that the space in the rubber hose between the hollow cylinder pieces is filled with a gel in order to fix the hydrophones in the hose.

Signal processing

In contrast to the Sonar 80, the Sonar 90 works with sensor fusion and integrated Target Motion Analysis (TMA). The system consists of modules, 40 of which are boards in E format or 20 in DE format, or a mixture of both. Each module performs a signal processing task . A computer cabinet takes 2 to 6 modules, some of them as a reserve. The system uses EPR 2300 32-bit processors with Motorola 68030 CPUs and ADSP 2100 digital signal processors. A typical signal processor card has a 30 MIPS processor array to carry out frequent calculations such as FFT , filtering and normalization with three digital signal processor macrocells, each with ADSP- 2100 processors with 240 kByte RAM . There are 70 different types of the total of 500 computer boards. The software is written in Ada .

All sonar antennas feed into a common fiber optic bus with three consoles: One for the active sonar with 8 Automated Target Trackers (ATT), one for the passive antennas (8 ATTs for DEMON, and 8 ATTs for LOFAR of the side and towing antenna) and one for the tactical picture using TMA and PRS. The system can pursue eight goals in the sensor network and supplement them with data from other sensors. The module for target classification SIP 3 of the Sonar 80 has been replaced by the APC module.

Active sonar

When the Bugsonar is actively working, the received data from CW and FM are processed in parallel in order to achieve faster results. The CW component is used to calculate the Doppler effect in order to determine the radial speed of the target, the FM component profiles the target lengthways and thus outputs the course angle and body length of the target. The active sonar is displayed in a B-Scope , with the data being displayed by two adjacent virtual signal cones. The computer outputs the speed of the target based on the course angle and Doppler, and a classification as to whether the contact is a submarine. Several CM50 / FM50 pulses or one CM300 / FM300 pulse are required for this. The transmission modes are: Omnidirectional (ODT), omnidirectional with three active signal cones (TRDT), each with any combination of 5 ms and 50 ms pulses; omnidirectional search in a sector (S-ODT), S-TRDT as a combination of both, and SDT as a sector search for fire control solutions, where only 300 ms pulses are used. Different frequencies are used depending on the target size, required resolution and location range. New mathematical processes are the basis for improved use of sonar power. Based on models of sound propagation, adaptive signal processing takes place, which takes geophysical conditions (salinity, temperature, density) depending on location, weather and season into account and is based on current three-dimensional maps of the ocean. Direction, distance, doppler and signal strength can be displayed on a PPI . The results of the last 5 pings can be displayed for each target. Up to 30 targets can be pursued at the same time. Two Kalman filters ensure a clean track when the target is maneuvering. By target correlation, false targets are eliminated. Up to 10 selected targets can also be displayed on the other sonar consoles. This means that both actively and passively located targets can be displayed on the consoles. The range setting of the displays is from 2 kyd (1.8 km) to 48 kyd (43.6 km), with six intermediate levels.

Passive sonar

Input noises from passive location are integrated and a map of the noise intensity distribution is created through beamforming. All bearing angles are transformed to geographic north, knowing your own course. The data from the nose, edge and trailing sonars are processed simultaneously in broadband and narrowband. The incoming sonar signals are pulled through an envelope curve demodulator , processed with a window function , subjected to a fast Fourier transformation , normalized and signal averaged . With narrowband processing, the signal is subjected to LOFAR and DEMON analysis. The former can classify the noise source based on machine and screw noises (ignition rate of the cylinders, number of cylinders, pumps, rotation rate of the shaft (s), cavitation, etc.). Subsequently, the signal is controlled by a fuzzy logic subjected to a demonstration analysis. Propellers generate intensity-modulated signals, which are detected by an algorithm through maximum search, measurement of the distances between the frequency lines, etc. This suggests 20 base frequencies, which are given confidence values ​​by a fuzzy logic. These are multiplied by the possible number of propeller blades and the results are also given confidence values. As long as the received noises are good enough, the number of blades and the rotational frequency of the drive of the contact can be output.

The Automated Target Tracking (ATT) also works with fuzzy logic in order to convert the bearing angle-time data into target courses. For this purpose, the broadband noise energy from a certain bearing angle is integrated and analyzed for every second. The information is then plotted in a waterfall plot; H. the time over the course angle. The greater the energy that comes from an angle, the clearer the curve, which runs from top to bottom like a waterfall. Since these local maxima probably represent the position of targets, trackers are initialized. The fuzzy logic calculates the presumed bearing angle to the target in the next time step based on the past bearing angle. If a suitable sound is actually found here, it is assigned to the track history of the target. New observations that cannot be assigned to an existing tracker lead to the initialization of a new one. If no contact is found at a predicted position, the tracker is penalized. Since there are two trust factors, one for the track and one for its history, which are only calculated every sixteen time steps, a loss of contact does not necessarily lead to the termination of the track, as noises can also cover each other. Most trackers that are generated by the false alarm rate are terminated because of too many penalty points. In this way, noise sources can also be kept apart if their bearing angles cross or touch.

Multiple Hypothesis Tracking (MHT) for Target Motion Analysis (TMA) is used to display the watercraft and other sources of noise in a top view on a raster scan scope . For this purpose, target movements are combined into non-binding tracks, non-binding because they are not displayed. Each new location at a certain bearing angle ensures that the hypothesis tree is intertwined. Narrowband analysis is used as an aid for the task of extracting, deleting and maintaining tracks. All frequencies transmitted by a given target (i.e. bearing angles) are therefore stored. The LOFAR analysis is used to determine whether it is a real target. If the characteristic frequency lines are suitable, the track is binding and displayed. The characteristic frequency lines also assign curves on the waterfall plot if these are interrupted, for example, by obscuration. In order to avoid a calculation catastrophe - the number of hypotheses increases exponentially to the number of contacts - penalty points and gating techniques are used.

For example, it is sufficient for the submarine to follow a star-shaped pattern to determine the course and position of all targets within range of the sonar. Depending on the scenario, it can take minutes to hours until the scenario is resolved and all targets can be tracked with position and speed vector on the PPI scope or raster scan scope. In the case of contacts that are located by the PRS 3-15, or by towing and side sonars at the same time, the course and position can be determined almost instantaneously. The broadband and narrowband data from passive location can be presented to the sonar operators for manual analysis. Up to 20 passive targets can be tracked automatically. New targets, regardless of whether they are actively or passively located, trigger a new target alarm.

The active sonar recognizes torpedoes by the air bubbles and the rapid target movement, otherwise the intercept sonar is available for this. The antennas determine the angle, frequency, pulse length, pulse repetition frequency and amplitude for distance estimation. Up to eight passive targets can be tracked simultaneously, and up to 10 signals can be classified at the same time, e.g. B. for torpedo warning, which are mapped as rays on the PPI. Of Atlas Elektronik still a patent for Splash positioning exists. According to this, airborne underwater running bodies can be located by the splashing noise during immersion with the help of a wavelet analysis , even before they have started the attack run underwater, in order to gain 5-20 seconds before the torpedo becomes active.

Range

When considering the location range of a sonar system, the passive sonar range is particularly important, as active location would reveal one's own presence. The passive location options depend on the sound power of the opposing vessel and the sensitivity of the own antenna. The latter reaches its limits when the vehicle goes down in the background noise. When locating submarines, the most difficult sonar target, their sound emissions on different frequencies are crucial for classification, but also for location itself, since broadband is integrated over the receivable frequency spectrum.

In principle, the volume of the submarine noise source is inversely proportional to the square of the frequency. Since there is usually a peak at 50–100 Hz, the volume is 6 dB lower at over 200 Hz. The low frequencies and their characteristic occurrence can also be located at low speed levels and used for classification. The discrete lines at 0.1-10 Hz are caused by the rotation of the propeller and are difficult to shield. Also, water hardly attenuates low frequencies, so that they carry very far. Frequencies up to 100 Hz are caused by the hull and the drive train. Here there is a peak at 50 or 60 Hz, corresponding to the generator frequency. In older submarines, even higher harmonics could be observed, i.e. integer multiples of the basic frequency (up to 5). In submarines that have been built since the late 1980s ( Los Angeles Flight III , Akula II etc.) there are no longer any peaks above 100 Hz, at least if they do not travel faster than about 8 knots . Modern boats like the Akula II class also use anti- noise to suppress noise. At higher speeds, the flow noises dominate, as these increase with the sixth square of the flow speed. Therefore, double speed means 64 times louder flow noise. According to the Ingenieurkontor Lübeck (IKL), the noise emissions of a diesel submarine that was developed in the mid-1980s (e.g. 211 , newer 209s ) with electric underwater travel are as follows (decibels above the logarithm of speed):

  • Noiseless up to 4 kn
  • From 4 to 8 kn from 0 to 8 dB, due to machine noise
  • From 8 to 21 kn from 8 to 30 dB, due to flow noise
  • From 21 to 22 kn from 30 to 40 dB, cavitation limit
  • From 22 to 30 kn from 40 to 45 dB, cavitating

Since the approximate frequency curves and speeds are also given, it can be seen that these boats are about 10 dB quieter than an Akula and 20 dB quieter than a Delta IV , each at about 6 kn. The noise development of the kilo class should roughly correspond to the Akula boats. According to calculations, a Los Angeles boat can locate an Akula within 4–11 km in the Barents Sea with a wind speed of 2 m / s if both are traveling 4–8 kts, with a Delta IV already approaching 7–35 km would be located.

According to the information provided by Atlas Elektronik, the 50 mm towed sonar was able to locate a "silent sub" with 3 dB in broadband on 6.3 km at 6 kts during tests off the coast of Crete in 100 to 500 m deep water. If the diesel boat listed above is used for electric travel, this corresponds to a target speed of 5 kn. Since the Akula should be about 10 dB louder, the distance law results in a detection range of about 20 km. Although the Mediterranean Sea off Crete offers worse conditions for a sonar system than the calmer and deeper Barents Sea, the detection ranges of the DTA 50 are about twice as high as those of the towing sonar of the 688 boats .

If one can believe the assessment of submarine expert Norman Polmar, the Severodvinsk-class submarines are just as much quieter compared to the Akulas as the Victor-I-class or Delta-I-class is louder. This would be around 25 dB more or less. Analogous to the above, the distance law can now be used to calculate 1.1 km at 5 kn target speed. The Seawolf - and Virginia are a little quieter as Polmar. Both also use the more modern TB-29A, which has been delivered since 2002, instead of the older TB-23 towing sonar of the 688 boats.

According to Atlas Elektronik, the range of the side sonar is around ten times lower than that of the tow sonar due to its own noise and poor antenna gain. What is a nuisance against Akula boats becomes a problem against the Severodvinsk class and the most modern conventional submarines. The above-mentioned development of the Improved Flank Array Sonar (IFAS) is therefore understandable.

Users

country image Type Commissioning number U-displacement length Remarks
SwedenSweden Sweden HMS Gotland Gotland class 1996 3 1,600 t 60 m Without towing and navigation sonar
IsraelIsrael Israel INS Dolfin Dolphin class 1999 4 + 2 1,900 t > 85 m Navigation sonar over torpedo muzzles
GermanyGermany Germany / ItalyItalyItaly  U34 Submarine class 212 A 2003 6 + 4 1,800 t 56 m Navigation sonar over torpedo muzzles
South AfricaSouth Africa South Africa SAS Charlotte Maxeke (S-102) Heroine class 2005 3 1,400 t 62 m Without towing and navigation sonar
GreeceGreece Greece / South Korea / Portugal / TurkeyKorea SouthSouth Korea PortugalPortugal TurkeyTurkey  ROKS Son Won-il (SS 072) Submarine class 214 2007 6 + 17 1,900 t 65 m Navigation sonar under torpedo muzzles

Individual evidence

  1. ^ A b c d Eric Wertheim: The Naval Institute Guide to Combat Fleets of the World: Their Ships, Aircraft, and Systems . US Naval Inst Pr, 2007, ISBN 1-59114-955-X , pp. 242 ff. passim .
  2. ↑ a b c d e f g h i j k l m n o p q r Norman Friedman: The Naval Institute Guide to World Naval Weapons Systems, 1997-1998 . US Naval Inst Pr, 1997, ISBN 1-55750-268-4 .
  3. ↑ a b c d e f g h i j k l m n o p q r s t u v Norman Friedman: The Naval Institute Guide to World Naval Weapon Systems . US Naval Inst Pr, 2006, ISBN 1-55750-262-5 .
  4. ↑ a b c d e Kevin Brinkmann, Jörg Hurka (ATLAS ELEKTRONIK GmbH): Broadband Passive Sonar Tracking . 39th Annual Meeting of the Society for Computer Science (GI), 2009.
  5. ↑ a b c d Joachim Beckh: Blitz & Anker, Volume 2: Information technology, history & backgrounds . Books on Demand GmbH, 2005, ISBN 3-8334-2997-6 , pp. 105 ff. passim .
  6. ↑ Patent DE 4041590 A1: Method for determining the depth of a vehicle , Stn Atlas Elektronik GmbH, publication date Aug. 28, 1997
  7. ↑ Patent EP 0962784 A2: Method for passive determination of target data , Stn Atlas Elektronik GmbH, publication date Dec. 8, 1999
  8. ↑ a b c d Dietmar Schneider, Dr. Christoph Hoffmann (ATLAS ELEKTRONIK GmbH): TOWED ARRAY TECHNOLOGY: DEVELOPMENT FOR A BETTER SONAR SYSTEM PERFORMANCE . Proceedings of the International Conference “Underwater Acoustic Measurements: Technologies & Results” Heraklion, Crete, Greece, 2005.
  9. ↑ Applications with the piezocomposite material MFC - energy from vibrations for the energy from vibrations for the transmission of telemetry data. (PDF) In: Thomas Daue, Jan Kunzmann; Smart Material Corp. 2013, accessed December 22, 2013 .
  10. ↑ Patent EP 1191351: Underwater towed array , ATLAS ELEKTRONIK GMBH, publication date October 15, 2008
  11. ↑ Patent DE 19518461 C1: Unterwasser-Schleppantenne , Stn Atlas Elektronik GmbH, published on June 13, 1996
  12. ↑ a b c Kevin Brinkmann, Jörg Hurka (ATLAS ELEKTRONIK GmbH): Narrowband Passive Sonar Tracking . GI Annual Meeting 2, 2010, p. Vol. 176 of LNI, pp 812-817 .
  13. ↑ a b c Anton Kummert (ATLAS ELEKTRONIK GmbH): Fuzzy Technology Implemented in Sonar Systems . IEEE JOURNAL OF OCEANIC ENGINEERING, October 2003, pp. VOL. 18, NO. 4, pp 483-490 .
  14. ↑ Patent EP 1376079 A2: Method for detecting airborne underwater running bodies , ATLAS ELEKTRONIK GmbH, publication date Jan. 2, 2004
  15. ^ VN Gorbachev: The Ability of Submarines to Defend Themselves Against Naval Operations in Coastal Waters . Paper from American-Russian Conference on Anti-Submarine Weaponry in Coastal Waters, Queenstown, USA, June 1994.
  16. ^ VN Parkhomenko: Solving the noise problem of nuclear submarines . Morskoy Sbornik No. 2, 1993, p. 36-40 .
  17. ↑ SSN Akula Class (Bars Type 971) Nuclear Submarine, Russia. In: Naval-technology.com. 2013, accessed December 22, 2013 .
  18. ↑ a b c E.V. Miasnikov: The Future of Russia's Strategic Nuclear Forces: Discussions and Arguments, Appendix 1: What is known about the character of noise created by submarines? In: Published by the Center For Arms Control, Energy, and Environmental Studies at MPTI. 1995, accessed December 23, 2013 .
  19. ↑ EV Miasnikov: The Future of Russia's Strategic Nuclear Forces: Discussions and Arguments, Appendix 2: Estimates of submarine detection ranges. In: Published by the Center For Arms Control, Energy, and Environmental Studies at MPTI. 1995, accessed December 23, 2013 .
  20. ^ A b Norman Polmar: Cold War Submarines: The Design and Construction of US and Soviet Submarines, 1945-2001 . Potomac Books Inc., 2005, ISBN 1-57488-530-8 .
  21. ↑ Norman Polmar: Ships and Aircraft of the US Fleet . US Naval Inst Pr, 2005, ISBN 1-59114-685-2 , pp. 561 .
  22. ^ SSK Manthatisi Class (Type 209/1400) Attack Submarine, South Africa. In: Naval-technology.com. 2013, accessed December 22, 2013 .