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Anti-Submarine Warfare (ASW); news and updates
Topic Started: Sun Jun 15, 2014 11:37 pm (1,155 Views)
Flipzi
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Photo: AgustaWestland wildcat ASW chopper (credit to photo owners)

Anti-Submarine Warfare

Anti-submarine warfare (ASW, or in older form A/S) is a branch of naval warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines.

Current technologies
There are a large number of technologies used in modern anti-submarine warfare:

Sensors
- Sonar / Acoustics particularly in active and passive sonar, sonobuoys and fixed hydrophones and in the reduction of radiated noise. Sonar can be mounted on the hull or in a towed array.
- Pyrotechnics in the use of markers, flares and explosive devices
- Searchlights
- Radar
- Low frequency spread-spectrum electromagnetic surface wave devices
- Active spread-spectrum magnetic techniques
- Hydrodynamic pressure wave detection
- Blue-green laser airborne and satellite LIDAR
- Electronic countermeasures and Acoustic Countermeasures such as noisemakers
- Passive acoustic countermeasures such as concealment and design of sound-absorbing materials to coat reflecting underwater surfaces
- Magnetic anomaly detection (MAD)
- Active and (more commonly) passive infra-red detection

In modern times forward looking infrared (FLIR) detectors have been used to track the large plumes of heat that fast nuclear-powered submarines leave while rising to the surface. FLIR devices are also used to see periscopes or snorkels at night whenever a submariner might be incautious enough to probe the surface.

The active sonar used in such operations is often of "mid-frequency", approximately 3.5 kHz. Because of the quietening of submarines, resulting in shorter passive detection ranges, there has been interest in low frequency active for ocean surveillance. However, there have been protests about the use of medium and low frequency high-powered active sonar because of its effects on whales. Others argue the high power level of some LFA (Low Frequency Active) sonars is actually detrimental to sonar performance in that such sonars are reverberation limited.

Weapons
Mines
Torpedoes, acoustic, wire-guided, and wake homing.
Depth charges
Rockets
Missiles
Anti-submarine net
Ramming

http://en.wikipedia.org/wiki/Anti-submarine_warfare

For a good jumpstart, please see this video;

Video 1: Combat in the Air 2/5 - Anti Submarine Warfare

http://www.youtube.com/watch?v=Hy3MDw0W8N0

Explanation on some of the ASW Sensors

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Air ASW efforts began in earnest during World War II to counter the dangerous submarine threat. The devastation and terror experienced earlier during World War I dramatically prioritized the requirement for effective ASW forces; including aircraft. The duelists, the aircraft and the submarine, have been locked into an intense chess match ever since World War II. With each new tactical or technological innovation for Air ASW, the submarine threat counters with either a new procedure or system. The three distinct historic phases of Air ASW include the World War II years, the Cold War period, and the Post-Cold War era.

ASW Sensors

Detecting the stealthy submarine starts with maintaining a tool kit of different sensors. Each sensor has specific applications that counters different submarine operations. Many of these sensors complement and corroborate each other to enhance ASW effectiveness. Air ASW sensors are divided into two basic types; acoustic and non-acoustic. In some foreign services, these acoustic and non-acoustic sensors are commonly referred to as wet-and dry-end sensors.

Non-acoustic sensors augment the detection capability provided by acoustic sensors. These sensors use radar to detect exposed periscopes and hull surfaces, electro-magnetic systems to intercept the radar emissions from submarines, infra-red receivers to detect the heat signatures of surfaced submarines, or Magnetic Anomaly Detectors (MAD) to sense small changes in the Earth's magnetic field caused by the passage of a submarine. This sophisticated technology is further enhanced by vigilant lookouts who are carefully scanning the turbulent ocean surface for submarine periscopes and wakes.

Radar Sensors

Radar sensors have been used since World War II for the detection of surfaced or snorkeling submarines. Back then, submarines relied upon their batteries for submerged operations. Eventually their batteries would become drained to the point where they were forced to return to the surface and operate their diesel engines to re-charge the battery. While surfaced, the submarine was extremely vulnerable to detection by both radar and visual sensors. The addition of a snorkel enabled the submarine to operate its battery-charging diesel engines while minimizing its exposure to radar and visual sensors. Additionally, the background clutter of the surrounding ocean waves limited radar and visual detection. Also, the development of submarine-based electro-magnetic sensors provided the submarine commander with suffficient warning to dive if approaching radar emissions were detected.

Eventually, nuclear submarines where developed which eliminated the need to periodically recharge the batteries. Despite this significant advance, not all nations were able to build nuclear submarines due to financial and technological reasons. Those nations which remain committed to diesel power have pursued technology which limits the number of times the submarine has to recharge its batteries. However, many submarine commanders must still use their periscopes to provide final visual classification of targets prior to attack. Because of this requirement for target verification, radar systems are still used to detect submarine periscopes.

Today's airborne radar systems must be lightweight yet sufficiently capable for ASW operations, long-range detection and surveillance of surface vessels, airborne navigation, and weather avoidance. For that purpose, many Air ASW radar systems use different radar frequencies, scanning speeds, transmission characteristics, pulse lengths, and signal processing methods that reduce background sea clutter and enhance radar returns from exposed pericopes and submarine hulls. The hostile submarine using electro-magnetic sensors, however, can still detect ASW aircraft radar emissions at a much greater distance than the aircraft can detect the submarine by radar. Nevertheless, the threat of radar detection is sufficient to keep the submarine submerged. Radar systems now used aboard U.S. Navy ASW aircraft include the AN/APS-115 (P-3C), AN/APS-124 (SH-60B), and AN/APS-137 (S-3B, some P-3Cs).

Magnetic Anomaly Detection (MAD) Sensors

MAD sensors are used to detect the natural and manmade differences in the Earth's magnetic fields. Some of these differences are caused by the Earth's geological structures and sunspot activity. Other changes can be caused by the passing of large ferrous objects, such as ships, submarines or even aircraft through the Earth's magnetic field. MAD sensor operation is similar in principle to the metal detector used by a treasure hunter or the devices used by utility companies to find underground pipes.

For ASW purposes, the ASW aircraft must almost be essentially overhead or very near the submarine's position to detect the change or anomaly. The detection range is normally related to the distance between the aircraft sensor ("MAD head") and the submarine. Naturally, the size of the submarine and its hull material composition normally determines the strength of the anomaly. Additionally, the direction travelled by both the aircraft and the submarine relative to the Earth's magnetic field is also a factor. Nevertheless, the close proximity required for magnetic anomaly detection makes the MAD system an excellent sensor for pinpointing a submarine's position prior to an air-launched torpedo attack.

In order to detect an anomaly, the MAD head of the aircraft tries to align itself with the noise produced by the Earth's magnetic field. Through this alignment, the noise appears as a near-constant background noise value which enables the operator to recognize any contrasting submarine magnetic anomalies from the background noise. However, any rapid changes in aircraft direction or the operation of certain electronic equipment and electric motors can produce so much aircraft electro-magnetic noise that makes the detection of the submarine's magnetic signature virtually impossible. Special electronic circuitry is enabled to compensate and null out this aircraft magnetic noise. Additionally, the MAD head is placed the farthest distance away from all the interfering sources. That is why the P-3C Orion aircraft has its distinct tail stinger or "MAD boom". On the S-3B, a similar MAD boom is installed and is electrically extended away from the aircraft during MAD operations. Additionally, the SH-60B extends a towed device called a "MAD bird" to reduce aircraft magnetic noise. With continuing advances in both compensation and sensor technology, the detection ranges for MAD sensors may be enhanced for the search and localization phases of ASW missions. Currently all naval ASW aircraft use variations of the AN/ASQ-81 MAD system. A few P-3C aircraft use an advance MAD system, the AN/ASQ-208, that uses digital processing.

Electro-Magnetic (EM) Sensors

Electro-Magnetic (EM) sensors passively scan the radio frequency spectrum for intentional electronic transmissions from hostile forces. These electronic emissions originate from land sites, ships, and aircraft.

They can also be detected from submarines. By comparison, Air ASW EM sensors are sophisticated versions of radar detectors used to sense police radar gun signals. The difference, of course, is that Air ASW EM sensors provide all the details necessary to classify and localize the type of electro-magnetic emission that has been detected.

Since the radio-frequency spectrum is extremely cluttered with both hostile, friendly, and neutral electronic emissions, ASW aircraft EM systems are designed to search mainly for radar signals. To further reduce the electronic clutter, signature libraries are used to selectively search for specific submarine radar signals while disregarding signals from friendly and neutral radar systems. Detection of electronic emissions, however, is dependent upon the submarine commander's gamble to operate the submarine radar. Although, EM systems are not normally one of the primary ASW sensors, its flexibility for detecting hostile aircraft and naval combatants at long ranges makes it an effective sensor for all air warfare missions. Its potential presence deters the operation of submarine radar systems forcing the submarine commander to rely on other less accurate sensors to find targets. EM systems installed on naval ASW aircraft include the AN/ALQ-78 and AN/ALR-66 series on the P-3C Orion, the AN/ALQ-142 on the SH-60B Seahawk, and the AN/ALR-76 on the S-3B Viking.

Infra-Red (IR) Sensors

IRsensors are used to detect the heat signatures that extend beyond the visible light spectrum. They are commonly called either FLIR (Forward Looking Infra-Red) or IRDS (Infra-Red Detection System). The major difference between FLIR and IRDS is that FLIR passively scans for IR sources forward of the aircraft whereas IRDS searches all around the aircraft. This passive sensor device must be cryogenically cooled in order to detect IR sources. The IR signature itself can be masked by warm waters and high humidity. When conditions permit, medium detection ranges can be obtained that are comparable or even better than normal visual search ranges. At night, the system works even better as long as there is a noticeable difference in temperature between the source and the background environment. IR systems for nighttime ASW operations have replaced the previous method of illuminating the ocean with either a searchlight or flares; active visual search methods. By using a passive system such as either FLIR or IRDS, the submarine commander has another dilemma to solve on whether to snorkel or surface during the night. Most ASW aircraft utilize the IR sensors not only for ASW, but also for maritime surveillance.

Visual Sensors

Many submarine contacts are still detected using visual scanning techniques. These techniques are sometimes augmented by sophisticated binocular and other electro-optical devices. Submarine commanders are still wary of being visually spotted and maintain a safe speed when their periscopes are exposed so that their telltale wake remains indistinct compared to the background sea clutter. The position of the Sun and the Moon as well as the direction of the ocean waves are all factors the submarine commander must consider in order to remain unobserved. In some regions of the world, phosphorescent marine organisms illuminate a submerged submarine allowing it to be visually spotted. Additionally, some aircrews may use night vision goggles to aid in visual detection at night.

Full detail http://www.fas.org/man/dod-101/sys/ac/asw.htm

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C295 Maritime Patrol Aircraft (MPA) / Anti Submarine Warfare (ASW) - credit to photo owners


Related articles;

Anti-Submarine Warfare
A PHOENIX FOR THE FUTURE
by John Morgan, Captain U.S. Navy
http://www.navy.mil/navydata/cno/n87/usw/autumn98/anti.htm

Anti-submarine warfare
http://en.wikipedia.org/wiki/Anti-submarine_warfare
Edited by Flipzi, Mon Jun 16, 2014 1:30 am.
Alfred Alexander L. Marasigan
Manila, Philippines
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by John Morgan, Captain U.S. Navy

The New ASW Assessment

There are three fundamental truths about ASW. First, it is critically important to our strategies of sea control, power projection, and direct support to land campaigns. The Chinese military strategist Sun Tzu recognized some 2,400 years ago that the best way to defeat an enemy is to attack his strategy directly. As the United States looks to refine its focus on forward presence and power projection from the sea, as envisioned in the 1994 Forward...From the Sea strategic concepts paper, the submarine threat that denies, frustrates, or delays sea-based operations clearly embodies Sun Tzu’s dictum and attacks our strategy directly.

During the 1982 Falklands conflict, for example, the Royal Navy established regional maritime battlespace dominance with a single submarine attack, the sinking of the Argentine cruiser General Belgrano by the nuclear attack submarine Conqueror. But the British were fighting at the end of a perilously thin, 8,000-mile long logistics lifeline, and themselves were extremely vulnerable to submarine attack. Had the single Argentine Type 209 submarine that got underway, San Luis, been successful in just one or two of its several attacks — which were stymied as a result of an improperly maintained fire control system — and sank or seriously damaged one of the two British small-deck carriers or several logistics ships, the outcome might have been very different. We must recognize that in today’s and tomorrow’s conflict scenarios, the submarine is an underwater terrorist, an ephemeral threat. It will force us to devote a great deal of resources and time, which we might not have.

Second, ASW is a team sport — requiring a complex mosaic of diverse capabilities in a highly variable physical environment. No single ASW platform, system, or weapon will work all the time. We will need a spectrum of undersea, surface, airborne, and space-based systems to ensure that we maintain what the Joint Chiefs of Staff publication Joint Vision 2010 calls “full-dimensional protection.” The undersea environment, ranging from the shallows of the littoral to the vast deeps of the great ocean basins — and polar regions under ice — demand a multi-disciplinary approach, subsuming intelligence, oceanography, surveillance and cueing, multiple sensors and sensor technologies, coordinated multi-platform operations, and underwater weapons. Most impor-tantly, it takes highly skilled and motivated people.

Finally, ASW is hard. The San Luis operated in the vicinity of the British task force for more than a month and was a constant concern to Royal Navy commanders. Despite the deployment of five nuclear attack submarines, 24-hour per day airborne ASW operations, and expenditures of precious time, energy, and ordnance, the British never once detected the Argentine submarine. The near-shore regional/littoral operating environment poses a very challenging ASW problem. We will need enhanced capabilities to root modern diesel, air-independent, and nuclear submarines out of the “mud” of noisy, contact-dense environments typical of the littoral, and be ready as well to detect, localize, and engage submarines in deep water and Arctic environments.

Read more about this article http://www.navy.mil/navydata/cno/n87/usw/autumn98/anti.htm


Submarine "ARA San Luis" (S-32)
http://en.wikipedia.org/wiki/ARA_San_Luis_(S-32)

Photo: artist rendition of San Luis (credit to http://operacoesmilitaresguia.blogspot.com/2013/02/o-ara-san-luis-da-guerra-da.html)
Edited by Flipzi, Sun Jun 15, 2014 11:56 pm.
Alfred Alexander L. Marasigan
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Submarine Warfare in World War 2

- plus anti-submarine warfare documentary

Video 1: Submarine Warfare in the Pacific in World War 2

http://www.youtube.com/watch?v=7mxzKuzN4wc

Video 2: World War II Submarine Warfare rare footage

http://www.youtube.com/watch?v=x8DxhS8wpoI

Video 3: U Boat War Documentary on the Submarine Battle of World War 2

http://www.youtube.com/watch?v=mJtKcUiWEms
Alfred Alexander L. Marasigan
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http://z6.invisionfree.com/flipzi

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A good discussion on anti-submarine warfare

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TACTICS 101:

ART 1 - THE FUNDAMENTALS
In Part 1 of our discussion about ASW, we learned the basics of naval oceanography, and in large part, how sound behaves in the subsurface ocean environment.
http://harpgamer.com/harpforum/index.php?/topic/3461-tactics-101-anti-submarine-warfare-asw-part-1/

PART 2 - THE TOOLS OF ASW
In Part 2, we moved to a basic examination of the tools of anti-submarine warfare (ASW), the sensors, the platforms, and the weapons.
http://harpgamer.com/harpforum/index.php?/topic/3527-tactics-101-anti-submarine-warfare-asw-part-2/

PART 3 - THE ASW CYCLE
http://harpgamer.com/harpforum/index.php?/topic/3605-tactics-101-anti-submarine-warfare-part-3/



The world's 10 best anti-submarine warfare (ASW) helicopters

2 January 2014

Helicopters with anti-submarine warfare (ASW) systems are widely deployed by naval forces as a means to counter submarines at long ranges. Naval-technology.com lists the 10 best anti-submarine warfare helicopters based on ASW equipment, range and endurance.

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http://www.naval-technology.com/features/featurethe-worlds-best-anti-submarine-warfare-asw-helicopters-4153353/
Edited by Flipzi, Mon Jun 16, 2014 12:36 am.
Alfred Alexander L. Marasigan
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ANTI-SUBMARINE WARFARE (ASW) CONTINUOUS TRAIL UNMANNED VESSEL (ACTUV)

The Anti-Submarine Warfare (ASW) Continuous Trail Unmanned Vessel (ACTUV) is developing an unmanned vessel optimized to robustly track quiet diesel electric submarines. The program is structured around three primary goals:

- Explore the performance potential of a surface platform conceived from concept to field demonstration under the premise that a human is never intended to step aboard at any point in its operating cycle. As a result, a new design paradigm emerges with reduced constraints on conventional naval architecture elements such as layout, accessibility, crew support systems, and reserve buoyancy. The objective is to generate a vessel design that exceeds state-of-the art platform performance to provide propulsive overmatch against diesel electric submarines at a fraction of their size and cost.

- Advance unmanned maritime system autonomy to enable independently deploying systems capable of missions spanning thousands of kilometers of range and months of endurance under a sparse remote supervisory control model. This includes autonomous compliance with maritime laws and conventions for safe navigation, autonomous system management for operational reliability, and autonomous interactions with an intelligent adversary.

- Demonstrate the capability of the ACTUV system to use its unique characteristics to employ non-conventional sensor technologies that achieve robust continuous track of the quietest submarine targets over their entire operating envelope.
While the ACTUV program is focused on demonstrating the ASW tracking capability in this configuration, the core platform and autonomy technologies are broadly extendable to underpin a wide range of missions and configurations for future unmanned naval vessels.

The program has four phases. During phase 1, the program refined and validated the system concept and associated performance metrics, completing risk reduction testing to inform program risks associated with submarine tracking sensors and maritime autonomy. In August 2012, DARPA awarded a contract for phases 2-4. The program plans the following in upcoming phases: Design a vessel (Phase 2); Build a vessel (Phase 3) and test the vessel (Phase 4). Operational prototype at-sea testing is expected in mid-2015.

http://www.darpa.mil/Our_Work/TTO/Programs/Anti-Submarine_Warfare_(ASW)_Continuous_Trail_Unmanned_Vessel_(ACTUV).aspx
Edited by Flipzi, Mon Jun 16, 2014 12:46 am.
Alfred Alexander L. Marasigan
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One of the new Maritime Patrol Aircrafts (MPA) with ASW capabilities


http://www.youtube.com/watch?v=l0smqcYsLjQ

Story http://w11.zetaboards.com/NDSFP/topic/10283080/1/#new
Edited by Flipzi, Mon Jun 16, 2014 12:55 am.
Alfred Alexander L. Marasigan
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getflipzi@yahoo.com

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