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Tactics 101: Anti-Submarine Warfare - Part 3


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TACTICS 101: ANTI-SUBMARINE WARFARE: PART 3 - THE ASW CYCLE

 

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.

 

In Part 2, we moved to a basic examination of the tools of anti-submarine warfare (ASW), the sensors, the platforms, and the weapons.

 

Now, in Part 3, we'll examine the ASW cycle, the methodology of detecting, locating, and attacking submarines.

 

A. DETECTION, LOCATION AND TARGETING

 

1. Detection

 

Initial detection of a subsurface contact, whether by active or passive means, is your first clue that there is a submarine in the area, or in the old parlance, a POSSUB (Possible Submarine) report is generated.

 

For passive sonar, confirmation of submarine detection is often made through receiving and analyzing the lowest frequency sounds, such as propeller noises, and will give you a general idea that the target is in fact a submarine, rather than say, a biological or just "magma displacement". ;) It will not tell you which navy the submarine belongs to, or what type it is.

 

Broadband noise is produced by a target's propulsion machinery, its propellers, the hull passing through the water, external fittings, etc. As a contact gets closer to the receiver, more and more information is gleaned as progressively higher frequency and lower strength sound becomes available, including narrowband sources. This combination of a ship or submarine's self-noise, both narrowband and broadband, form its "acoustic signature" and can be exploited by to identify a contact as a submarine.

 

Initial detection by active sonar provides even less information, simply telling you that there is something there underwater. The determination of the identity of that "something" is a function of operator training and experience.

 

Direct Path

 

As discussed in Part 1, the direct path is the simplest acoustic propagation path and is essentially a straight line path between the sonar source and the target.

 

Due to the reduced opportunity for signal propagation loss and the fact that there is no reflection of the sound, a direct path sonar contact may be the easiest to obtain and analyse, but it also presents the shortest range passive detection opportunity (typically less than 10 nautical miles).

 

Because it is so short ranged, any surface ship obtaining a direct path detection of a submarine target is already in significant danger. It is extremely likely that the submarine has already been tracking the ship for some time, working a fire control solution, and is now approaching for the kill. It is the "oh, crap" detection scenario.

 

Bottom Bounce

 

With the bottom bounce technique, active sonar energy is directed towards the bottom. Steeply inclined sound ray paths are affected to a lesser degree than the shallower (in some cases, nearly horizontal) paths of other methods (e.g. surface duct, convergence zone, etc) and so there is less transmission loss and less potential for shadow zones.

 

Bottom bounce is only useful, however, where the ocean floor has a hard, flat surface (where you can get a good reflection) and its a poor choice where the bottom is rocky or soft mud (where sonar is dispersed by reverberations or absorbed). The Barents Sea, for example, has excellent conditions for bottom bounce sonar technique.

 

Because it typically involves the use of active sonar, however, bottom bounce carries a significant amount of risk in the ASW role and is a technique generally reserved for very specific scenarios where passive sonar simply isn't sufficient.

 

Convergence Zone (CZ) Detections

 

As discussed in Part 1, convergence zones (CZ) are areas where refracted sound in deeper water can focus at the surface, typically at predictable intervals. The first CZ, for example, typically develops at about 30-33 nautical miles. The second CZ might form at 60-66 nm, a third at 90-99 nm, and so on.

 

The extent of CZ formation, or whether a CZ forms at all, is naturally dependent on whether sound can propagate far enough or deep enough, which in turn is dictated by environmental factors, notably water depth, temperature, etc.

 

In most cases, you are perhaps unlikely to get a detection beyond the first CZ. This is, under most conditions, a quite distant sonar contact in any event (keeping in mind, of course, that the CZ phenomenon can result in some pretty extraordinary sonar ranges). A contact would often have to be very loud and/or your passive sonar equipment very sensitive to achieve second and third CZ detections.

 

Also, a CZ detection will not usually provide any positional information on the target (i.e. you just get a bearing), negating the possibility of employing a long range ASW weapon against it. And, finally, a CZ detection tends to be a fleeting one. Once the target moves out of the CZ, or into a shadow zone, contact is often lost.

 

Sonobuoy Fields and Search Patterns

 

Using sonobuoys alone for an acoustic search is known as a "cold pattern". Since sea temperature, pressure (a function of depth) and salinity all affect the way in which sound travels through the water, those factors need to be determined for an effective cold pattern.

 

The first sonobuoys dropped from a P-3 Orion might therefore be, for example, a SSQ-36 and a SSQ-57, in order to establish local ocean conditions. The SSQ-36 is a bathythermograph sonobuoy used to get a temperature profile, while the SSQ-57 is a passive, omnidirectional "calibrated collection" sonobuoy, used to acquire ambient noises roduced by marine life and other ocean sources.

 

Once local conditions have been established, the aircraft might move to laying a field of active and/or passive sonobuoys.

 

The layout of a sonobuoy field will depend on what kind of search pattern is employed. The following are some examples of search patterns, which could be used to sow sonobuoy fields or conduct a radar/FLIR/MAD search, each of which indicates a commence search pattern (CSP) point.

 

The parallel pattern is most desirable when the target is assumed equally likely to occupy any part of the search area.

ASW_parallel_search_pattern.gif

Image credit: Journal of Simulation (2006) 1, 29-38.

 

The creeping line pattern is typically employed when the target is more likely to be in a particular end of the search area.

 

ASW_creepingline_search_pattern.gif

Image credit: Journal of Simulation (2006) 1, 29-38.

 

When the point of last contact is well known, or established within close limits, the square or sector search pattern is preferred. The square pattern is used when uniform coverage of the search area is desired.

 

ASW_square_search_pattern.gif

Image credit: Journal of Simulation (2006) 1, 29-38.

 

The sector search pattern is used where the target is difficult to detect.

 

ASW_sector_search_pattern.gif

Image credit: Journal of Simulation (2006) 1, 29-38.

 

Finally, when a target is fast moving or when a strong current is present in the search area, the barrier patrol search pattern is preferred (its CSP is either starting point). This was the pattern used extensively during the actual Bay of Biscay U-boat war.

 

ASW_barrier_search_pattern.gif

Image credit: Journal of Simulation (2006) 1, 29-38.

 

Although the greatest threat to a submarine is likely that posed by aircraft, it is by no means a sure thing that the aircraft will detect, locate, and successfully prosecute a submarine contact.

 

The sound of an aircraft coming close enough to attack (or the splashes from its dropped sonobuoys) can be detected by a submarine, particularly if the sub has a very sensitive passive sonar, such as a towed array.

 

And, since the submarine has better, more constant access to the ocean's environmental conditions, it can use this information to exploit weaknesses in the aircraft's sensor net. For example, by changing speed and direction, or by dropping below the thermal layer. Actively pinging sonobuoys can be mapped and avoided, or alternatively, hide directly beneath an active sonobuoy. This trick takes advantage of the fact that the active sonar pings move outward from the buoy like the rings from a tossed pebble, and so sitting underneath the buoy can shield the submarine to some extent.

 

2. Location and Identification

 

The next step is localizing the target. With active sonar, this is largely a simply exercise, but of course employing active sonar will almost always alert the enemy to your presence and so carries with it more than a little risk. Using passive sonar only, localization can still be accomplished by a number of means, including:

 

Target Motion Analysis (TMA)

 

An initial passive sonar contact typically provides only a bearing to the target, and tells you nothing about distance (range) or speed. The contact may be close by, creeping along at only 5 kt, or twice as distant, and moving at 10 kt.

 

Using only passive sonar, target motion analysis (TMA) is a mathematical process by which a contact's course and range can be estimated using timed readings of the contact bearing and an estimate of its speed. Each estimate is (hopefully) more accurate than the one previous, and eventually the estimation will be accurate enough to reliably predict the next bearing. TMA is thus, essentially, an initial approximation of target range, course, and speed. The closer the ensuing predictions come to reality, the more likely it is that the approximation is an accurate one.

 

Suffice to say, any target whose bearing is changing rapidly is quite close and needs to be localised in a hurry. Conversely, a distant target will show almost no change in bearing over time. (The same can be said, of course, for target that is exactly parallel, but its bearing will change as you change course even slightly).

 

TMA is a tedious procedure, one that can consume a lot of time and create considerable frustration, but it is certainly more stealthy than energizing an active sonar and can eventually produce a suitable firing solution. Initially, TMA calculations involved only a paper plot, used to determine short range fire control, and later evolving into a computerised system using software target tracking that can project a target's position ahead in time and be sufficently accurate to control wire guided weapons.

 

Limitations to the TMA technique include: contact must be maintained over a period of time; all contact bearings must be assumed to come from the same target over that period of time; and maneuvers must be built into own ship track in order to resolve ambiguities.

 

Beyond a certain range, of course, passive TMA techniques cannot reliably produce an accurate solution. For example, for convergence zone (CZ) detections, the only data typically available from passive sonar is a bearing. Range, course, and speed are practically impossible to determine. And, since a CZ contact is easily lost, the TMA solution clock would have to be reset and a new solution started from scratch each time.

 

LOFARGRAM

 

A Low Frequency Analysis and Ranging Record Gram (LOFARGRAM) plot can be generated where signal strength data can be gathered from non-directional passive sonobuoys.

 

The plot looks much like a waterfall display, and can be used be determine such identifying information as blade rate. This is a fairly complex exercise, however, and requires a detailed understanding of target signatures.

 

An example of a LOFARGRAM

lofargram.jpg

Image credit: Defence Science and Technology Laboratory (Dstl), UK Ministry of Defence.

 

Triangulation using DIFAR Sonobuoys

 

Here, each DIFAR buoy transmits a compass direction for each of its hydrophones and the operator can then determine which element on the buoy has the highest signal strength.

 

Target Identification

 

Although precise identification of the target may matter considerably less during wartime, when any unknown submarine contact found outside a recognized patrol area or transit lane may be assumed hostile, it is still of some value, especially when multiple targets present themselves. Identifying the contact can provide information about the threat it poses and help determine the application of rules of engagement (ROE) or an engagement priority. For example, identifying one of two submarine contacts as an Oscar II class SSGN, and the other as a Charlie class SSGN, may be convincing evidence of their threat priority.

 

At longer ranges, narrowband sources can be used to begin generating a picture of what the target might (or might not be). For example, during the earlier days of the Cold War, Soviet nuclear submarines could be broadly identified by their propulsion plants as follows:

 

Type 1 reactor plant: First generation nuclear subs, including the Hotel (Project 658) SSBN, Echo (Project 659/675) SSGN, and November (Project 627/645) SSN classes

Type 2: Victor (Project 671) SSN and Charlie (Project 670) SSGN classes

Type 3 (twinned Type 2 plants): Yankee (Project 667) and Delta (Project 667B) SSBN classes

Type 4: the Papa (Project 661) class SSGN

Type 5: the Alfa (Project 705) class SSN

Type 6: Sierra (Project 945) SSN, Oscar (Project 949) SSGN, and Akula (Project 971) SSN classes

Type 7: Typhoon (Project 941) class SSBN

 

More precise identification will require increasing analysis of a target's noise signature and usually requires fairly close quarters proximity between the target and the sensor, so that your classification becomes more refined over time.

 

Improved sonar processing techniques now make it possible to detect and demodulate target noise to identify it by measuring its shaft or propeller blade rate (blade rate tonals). Also, as a note of interest, the more blades, the more likely the contact is a submarine (as commercial merchant ship propellers have only three or four blades, while warships often have five).

 

The twin shafts and propellers of the Arleigh Burke class Aegis destroyer USS Curtis Wilbur (DDG-54)

Curtis_Wilbur_DDG54_props.jpg

Image credit: Federation of American Scientists.

 

Many older Soviet/Russian nuclear powered submarines, such as the Yankee (Project 667), Delta (Project 667B), Papa (Project 661) classes, have five blades. So do some older diesels, including the Swedish Vastergotland (A17) class. The Soviet/Russian diesel-electric Kilo (Project 877) class has six, while the later Project 636 variant of the Kilo and the newest Lada (Project 677) class SSK both have seven blades.

 

Many other modern submarine designs employ seven blade propeller systems, including, for example, the Soviet/Russian Typhoon (Project 941) SSBN, the Victor (Project 671) SSN (though some of the Victor III (Project 671RTM) variant were unique in having two four-blade props mounted in tandem), and the Akula (Project 971) SSN; the US Navy's Los Angeles (SSN-688) attack sub; the Chinese Type 039 (Song) and Type 039A (Yuan) class SSKs, and its Type 093 (Shang) SSN; and most newer European diesels, such as the Dutch Walrus SSK.

 

The 7 blade, skewed propellers of the Chinese Type 039 (Song) class SSK (this is the type that shadowed the US Navy's carrier Kitty Hawk in October 2006, surfacing within 5 miles - uncomfortably close - apparently without having been detected).

Song_Type039_props.jpg

Image credit: Chinese Military Aviation.

 

It probably should be noted that blade noise among Soviet/Russian submarine types dropped dramatically after Japanese electronics company Toshiba and Norwegian company Kongsberg sold advanced milling machinery and control equipment to the USSR in the mid 1980s. (And, of course, the treachery of John Walker).

 

Listening to and recording a submarine's unique sonar signature in peacetime can permit a navy to develop a library of what the other guy's submarines sound like, so much so that it is eventually possible to identify a submarine contact not only by its class or type, but by name!

 

3. Targeting

 

The final step in the ASW cycle is targeting, that is, developing a sufficiently accurate picture of the submarines location and movements to mount an attack that has a high probability of success.

 

In the targeting phase, final localization of a submerged target is often accomplished using active sonar (either active sonobuoys, echo ranging, or an active dipping sonar), or magnetic anomaly detection (MAD) gear. An aircraft that has localised a target will typically drop a smoke flare to mark its position, and then come around for a second pass to drop the weapon.

 

Also, as discussed in Part 2, there are a number of other sensors typically available to an ASW aircraft that can provide both detection and location of a submarine contact when it is contact is surfaced, snorkeling or traveling at a shallow depth, including visual means, radar, and infra-red (IR).

 

Active means of detection are not usually exercised during encounters between opposing submarines, where an attacking submarine will typically want to maintain stealth throughout the engagement.

 

B. ENGAGEMENT

 

1. Airborne Attack

 

Aircraft, and in particular, helicopters, are a God send to the ASW surface ship. They provide a way to search for, detect, locate, engage and destroy submarine targets at ranges well beyond the ship's own sensor envelope, while simultaneously avoiding the submarine's own weaponry.

 

Modern ASW helicopters also have their own suite of dedicated sensors, including surface search radar (useful for spotting periscopes and snorkels), MAD gear, dipping sonar, and/or sonobuoys, not to mention the means to destroy a submarine with lightweight torpedoes or depth charges.

 

When used in concert with shipboard sensors, especially long range passive towed arrays, the helicopter is a formidable ASW tool, perhaps the most formidable of them all. Its ability to hover precisely over a contact, dip a sonar, or tend a sonobuoy field, and operate from just about any ship that can host a helipad, is a testament to its flexibility. About the only weaknesses of the helicopter are its limited endurance, relatively slow speed, and small payload, but these are just small factors in comparison.

 

Where helicopters are lacking, fixed wing maritime patrol aircraft (MPAs) make up for it. They invariably have long endurance, considerable payload, and better speed.

 

2. Stand-Off Attack

 

A stand off attack against a hostile submarine is always the preferable method of engagement, whether this is having your helo dump lightweight torpedoes from a position far ahead of the formation; sending an ASROC on its ballistic trajectory; or launching a heavyweight torpedo on a dogleg course that exploits wire guidance and approaches from a different bearing.

 

The advantage of stand off attack lies principally with being able to rapidly engage a submarine outside the effective range of its own weapons, and sometimes, beyond the effective range of its own sensors.

 

3. Close Range Attack

 

A close range engagement with a submarine is a dangerous affair, one that more often than not ends up with both the hunter and the hunted switching positions.

 

An attack from a position in the target's baffles is one exception, in which case the attacker is already in the best possible position - the undersea equivalent of six o'clock high. If your opponent has a less capable passive sonar, maneuvering into an advantageous position is considerably easier and you may get much closer to him without being detected. If your passive sonar capabilties are about equal, however, then its really going to be quite a long, careful dance as you approach, followed by a frantic, desperate getaway.

 

The other close range option is a shipboard, "over the side" torpedo launch, in which case you are likely already in a worst case scenario. A hostile submarine has somehow managed to penetrate your screen and you are now trying to take last ditch, desperation measures to force him to maneuver by shooting your own torpedoes down the bearing of the contact (or worse, the bearing of an incoming weapon).

 

C. ANTI-SUBMARINE WARFARE (ASW) TACTICS

 

1. Tin Cans: The Surface Ship Sub Hunter

 

Since the noise of a surface ship formation (aka the "thundering herd") produces a lot of ambient noise, and may drown out or mask the noise of an enemy submarine, or otherwise degrade own passive sonar performance, the surface ships with the best passive sonars (typically those equipped with towed array sonars) typically operate at some distance away from the main body of the formation.

 

This stand off distance is typically about 10 to 30 nautical miles (nm), and frequently, out to the range of the first convergence zone (CZ). Units with less capable passive gear (e.g. a hull sonar but no towed array) tend to be stationed closer to the main body, with those ships equipped with only active sonar the closest of all.

 

ASW escorts often employ "sprint and drift" tactics. The "sprint" involves racing ahead at high or flank speeds to the leading edge of their assigned patrol sector, and then slowing to creep speed (typically below 10 knots, or slower) to conduct the "drift".

 

The sprint phase, of course, is noisy, but necessary in order to keep pace with the formation. The drift phase, however, cuts self-noise produced by revving engines, racing propeller screws, cavitation, and the noise of the hull passing through the water. In this fashion the ship can optimise the performance of its own passive sonar.

 

One might wonder why ASW ships bother to sprint at all, but rather, why not just creep from place to place to both optimise your own passive sonar and, at the same time, make the submarine's job of finding you harder?

 

Well, firstly, of course, the naval surface ship group is typically on a timetable and more often than not, a strict one. HQ wants you to put that group on station in a particular place, establishing force presence, conducting sea control, or pounding the enemy, and the guy right above you in the pay scale no doubt wants it done yesterday. And since the primary objective of your surface group is rarely blue water ASW, there are other more pressing concerns that require you to move at best speed. Sprinting will allow your ASW ship to thus keep up with the "thundering herd".

 

Secondly, there is truly an ASW method to the sprint and drift madness. Placing the most capable ASW assets on stations that are well removed from the noise of the main body, and in locations that either flank or are ahead of your group's intended path, puts those assets in the best possible position to detect enemy submarines.

 

In most cases, diesel-electric submarines have little opportunity for engaging a surface group from the sides or rear. They simply lack the submerged speed and endurance to do so. And, while nuclear powered submarines have both the speed and the endurance, approaching a surface group from the sides or rear would necessitate high speed maneuvering.

 

Speed, as we have already discussed, is noisy and degrades own sonar performance. Simply put, in the subsurface battlefield, noise kills. Therefore, "nuke boats" will also try to place themselves in the path of an enemy surface group, again right where your ASW escorts hope to find them.

 

2. Knife Fight in a Phone Booth: Submarine versus Submarine

 

The baffles are the area around a vessel in which its sonar is ineffective, forming a blind spot or dead zone. For most ships and submarines, this involves a cone about 15 degrees wide extending aft from the stern, in water disrupted by the screws and the vessels own passage.

 

Submarine_baffles.png

Image credit: Dan Short (DanMS).

 

An effective tactic for submarines, especially, is to close on a target, in the area of its baffles, and then shoot a torpedo from close range. There is virtually no opportunity for counter-attack or escape. Nuclear submarines, with their near limitless endurance and high speed capability, are especially good at exploiting this tactic. Even when you have no intention of attacking, placing your vessel in the baffles of the enemy can permit you to track him, trail him, and remain undetected.

 

There are a few tactics which can help defeat this approach. Turning your ship, or submarine, suddenly through 90 to 360 degree turns (the famous "Crazy Ivan") will place your sensors so as to listen down your former baffles.

 

In the following image, a Soviet Project 671RTM (NATO Victor III) class nuclear attack submarine has turned to port to check his baffles. The trailer, a US Navy Sturgeon (SSN-637) class boat, having detected the "Crazy Ivan" maneuver, has stopped his screw and gone quiet in an effort to maintain the subterfuge. If he is successful, the Victor III will make a complete 360 degree turn, around the Sturgeon, and then return to his original course, having never detected the drifting American sub. (Also visible is the Sturgeon's streamed towed array).

 

Trailing.jpg

Image credit: Jim Christley, "Trailing", subart.net

 

On the down side, any abrupt course change will also produce a pocket of disturbed water, called a "knuckle" that will act as a blind spot for both active and passive sonar systems. Scott Gainer says it still beats a torpedo enema anyday, though, and its difficult to disagree. :lol:

 

If more than one ship is traveling together, they can periodically turn and search each others' baffles using a crossing maneuver. And, when on the attack, one ship can stand off and conduct a search while the other deploys ASW weaponry, in order to avoid the submarine slipping under and escaping through the attacker's baffles, or during "blue outs" caused by weapon detonations (a "blue out" is a disruption of the sound path caused by the loud and sudden release of acoustic energy and bubbles in an underwater explosion).

 

Sonobuoys, dropped from the air or from ships, and helicopter dipping sonar employed to the rear of a formation, in the area of its baffles, can together provide a good plan to counter any approach from the rear.

 

3. Most Feared: the ASW Aircraft

 

The aircraft - whether fixed wing or rotary wing (helicopter) - is without a doubt one of the best tools in the ASW arsenal, perhaps the penultimate "force multiplier" from an ASW perspective. While the traditional ASW hunters - surface ships and submarines - have an equal (or better) chance of becoming the "hunted", the aircraft is perhaps the only weapon against which the submarine has little recourse (though even this is changing, more on that later).

 

Even for aircraft, however, the task of searching a vast ocean for a small, likely submerged, target is a hugely daunting task. And, as I've mentioned before, it can be pretty boring until you actually find something.

 

The principal advantage of an aircraft in the ASW role is speed, as compared to other platforms: speed in getting to the patrol area, speed in searching that area, and speed in prosecuting a contact.

 

Helicopters

 

Commensurate with the expanding size of the Soviet submarine fleet in the 1950s came a realization within the US Navy that its own increasing sonar detection ranges were outstripping its ASW engagement range. In particular, the RUR-5 ASROC (Anti-Submarine Rocket) then under development would not have the range to take advantage of the capability of the SQS-26 hull sonar.

 

A solution was found in the QH-50 DASH (Drone Anti-Submarine Helicopter), a small coaxial rotor equipped and unmanned helicopter which could operate from ships too small to have extensive aviation facilities, and moreover, operate in bad weather, even up to Sea State 6. (Something helo pilots did not (and do not) look forward to). Spooling up and taking off within two minutes of engine start, the DASH could deliver two Mk 44 lightweight homing torpedoes or a single Mk 17 nuclear depth charge to a sonar contact up to 22 miles away.

 

A QH-50A DASH operating off the Fletcher class destroyer USS Hazelwood (DD-531)

QH-50_A_DASH.jpg

Image credit: Gyrodyne Helicopters.

 

To illustrate the urgency of the Navy's desire for ASW stand-off weapons, production of the DASH was authorised a full year before the first model had ever taken to the air. By late 1963, funding had been approved for production of three QH-50C aircraft for each of the Navy's 240 FRAM I and II destroyers.

 

High attrition rates and the intervention of a non-ASW war in Southeast Asia (Vietnam, of course) led to the premature demise of the program in 1970, but the versatility of the shipboard ASW aircraft had clearly been established.

 

Ship based helicopters continue to be one of the most useful and flexible of ASW platforms, especially in terms of their multi-mission nature and ability to move out ahead of their host ship, thereby extending the range of the defensive zone. A modern naval helicopter can be packed with ASW relevant sensors - sonobuoys, a dipping sonar, radar, FLIR, ESM, etc - and can carry enough weaponry for one or two engagements, typically a pair of lightweight torpedoes.

 

The dipping sonar is the ASW helicopter's forte - the ability to hover right above a suspected enemy submarine, hammer it with active sonar, and thereby precisely determine its position as a prelude to a weapon drop. As we've learned throughout this Tactics 101 discussion, a submarine whose stealth has been compromised can quickly find itself in a world of hurt.

 

Active dipping sonar deployed from helicopters are the answer to the threat from quieter submarines in coastal areas by employing much lower frequencies, coupled with new transducer and beamforming technology.

 

Cold War ASW Icon: the P-3 Orion

 

The Lockheed P-3 Orion is perhaps the iconic symbol of airborne ASW during the Cold War era, certainly setting the standard for NATO maritime patrol and reconnaissance. A testament to the importance placed on the Orion's role by the US Navy was the fact that, at the height of the Cold War, the Navy operated about 26 active Patrol Squadrons (each with nine aircraft) and 13 Reserve Squadrons.

 

Although it first flew in 1958, the Orion continues to form the mainstay of US Navy fixed wing ASW and maritime patrol and reconnaissance capabilities, although in recent years the emphasis has shifted more toward the intelligence, surveillance and reconnaissance (ISR) role. (By 2001, for example, the previously mentioned squadron numbers had been cut to less than half). More on this in a bit.

 

The P-3 Orion with its weapons bay doors open

p-3_orion-1.jpg

Image credit: Global Aircraft.

 

A P-3 Orion crew typically consists of the following members:

 

* Three pilots, designated 1P, who is the aircraft commander and makes the tactical decisions; 2P, who monitors the aircraft's systems; and 3P, who is a new Orion pilot and comes straight from the Fleet Readiness Squadron;

* Two flight engineers;

* Tactical coordinator (TACCO);

* Navigator/communications operator;

* Two acoustic operators (Sensor 1, responsible for active sonobuoys, and Sensor 2, responsible for passive sonobuoys, although there is a lot of cross over);

* Non-acoustic operator (Sensor 3); and an

* In-flight tech/ordnance crewman.

 

Why three pilots? Flying at low level over the ocean for long periods of time, monitoring a myriad of instruments and maneuvering constantly to put the aircraft in a favourable position for the detection of submarines, is hard work. Three pilots are in fact probably the minimum necessary for most missions. Fortunately, the cockpit is spacious. During night missions, a curtain separates the cockpit from the remainder of the cabin, allowing the flight crew to concentrate on their instruments.

 

Moving toward the rear, the TACCO's station just outside the cockpit on the left. He recieves information from the three sensor operators and passes it to the cockpit so that the pilots can position the aircraft advantageously for an attack or sonobuoy drop. The TACCO is responsible for search tactics and tactical control. His console is dominated by a large screen showing the locations of sonobuoys, surface contacts, and the aircraft, as well as possible submarine contacts.

 

Sonobuoy information used to be recorded on two 16 channel AQH-4 analog magnetic recorders, each weighing nearly 300 lbs and providing only two hours' recording time, but this was replaced by an 80 lb AQH-13 system using Digital Tape Format (DTF) cassettes that offer four hours of recording time per cassette.

 

On the TACCO's right hand side is the Navigator/Comms, who is responsible for all navigation and communications duties.

 

Further down on the right side sits Sensor 3, the operator who processes information gathered by the radar (the APS-137 is the most recent type), forward looking infra-red (FLIR), the MAD and ESM. His console has a large radar display for the APS-137, which has four modes: periscope; weather; surface search; and navigation; and can effectively track 32 contacts. Right above the radar display is the FLIR display.

 

Behind Sensor 3 on the left and seated facing out of the P-3 (all other crew members sit facing forward) are Sensors 1 and 2, who process sonobuoy data from the sonobuoys. All of the information received from the sonobuoys is channeled into the UYS-1 Single Advanced Signal Processor (SAPS). Although Sensor 1 is technically responsible for passive buoys and Sensor 2 for active types, both can process the information from either type. A maximum of 32 sonobuoys can be monitored simultaneously (it used to be only four on the original P-3A), but only if they are all passive. Returns from the buoys are displayed on a screen, looking much like a green snow blizzard. When not actively engaged in ASW efforts, both Sensors 1 and 2 act as observers looking out of the aircrafts windows and as such, both are also qualified photographers.

 

The locations of sonobuoys dropped by the aircraft must be constantly updated, since getting a target bearing from a buoy is only useful if the correct location for the buoy is known. In order to correctly plot a buoy's position for the benefit of the TACCO, it is necessary to take into consideration the aircraft's altitude, air speed, and the wind characteristics. The drift of the sonobuoy is reported by an On Top Position Indicator (OTPI), which reports the information back to the aircraft. Information collected by the buoy, either from active (pinging) or passive acoustic means, is transmitted to the aircraft in the VHF band (over a number of channels). The TACCO uses the ASQ-114 digital computer, with its memory loaded with a large number of submarine acoustic profiles and radar and radio signals for ESM, to identify targets.

 

Halfway along the aircraft is the sonobuoy rack and chutes, with an observation position on either side of the fuselage. This is the domain of the In-flight Tech and Ordnance crew member, who is responsible for in-flight repairs of the electronics, and for preparing sonobuoys for drop. During the aircraft's transit to the patrol area, he inserts the Cartridge Actuated Device (CAD, a pyrotechnic firing device that launches buoys from their tubes, leaving behind the smell of cordite and a little smoke) and "channelizes" (assigns VHF channels) the sonobuoys in their rack.

 

The P-3C can carry 84 sonobuoys, of which 48 are pre-loaded from the outside before takeoff and 36 are carried in the cabin. In the cabin there are three "A size" launch tubes and one larger "B size" tube (for use without cabin pressure).

 

Behind the sonobuoy rack area is the crew rest position and galley.

 

So how has the Orion's mission changed since the Soviet submarine threat has all but vanished?

 

Turns out the P-3 Orion is more valuable than ever, but in a different role than traditional ASW and maritime patrol, as illustrated by the fact that it was responsible for shooting perhaps a couple dozen Standoff Land Attack Missiles (SLAMs) over the Balkans during Operation Allied Force in 1999 and during Operation Enduring Freedom in 2001; and as well, during Operation Iraqi Freedom in 2003, Orions were engaged in supporting the advance of ground forces toward Baghdad, warning them of enemy activity ahead, locating enemy armored vehicles at night, and making the initial detection of the burning oil fields at Ramallah; supporting US Navy SEAL and British Royal Marine commando operations to seize Iraqi oil terminals before they could be sabotaged; were involved in the rescue operation for captured soldier Pfc Jessica Lynch; aided in intercepting ships trying to smuggle oil out of Iraq; and provided targeting to a USAF AC-130 gunship so it could destroy some Iraqi patrol boats.

 

Submarine Self-Defense against Air Attack

 

How can a submarine defend itself from air attack?

 

Historically, or at least since the tide turned during the Battle of the Atlantic, a submarine's only defense has been to "run silent, run deep". But in any case, run. Gone are the days of the U-boat's Turmumbau flak guns.

 

The idea of submarine self-defense against aircraft never went away, however. The Soviets, for example, have been known to equip their diesel-electric types, particularly the Kilo (Project 877/636) class, with shoulder launched, short range heat seeking missiles, due to concern that they might be caught on the surface. The launcher and missiles are typically stored in a watertight container located between the snorkel and the radio antenna masts in the sail. The earlier Type 877 had a SA-N-5 (Strela) launcher and 8 missiles, while the Type 636 has the more capable SA-N-8 (Igla-1M) launcher and six missiles.

 

There have also been several efforts aimed at coming up with a way of launching a missile from a submerged submarine against a hostile aircraft. For example, the American DARPA program of the late 1970s for a Self-Initiated Anti-aircraft Missile (SIAM). More recently, the German Navy looks to adopt the IDAS (Interactive Defence and Attack System for Submarines): a fibre optic guided adaptation of the air launched IRIS-T short range missile, which can be launched from a torpedo tube and is due to arm Germany's Type 212 submarines from 2014.

 

The IDAS missile breaking the surface after launch from the Type 212 sub U-33

IDAS_launch_U-33.jpg

Image credit: Aviation Week.

 

D. ENDGAME: EVASION, DECOYS, AND COUNTERMEASURES

 

It goes without saying, of course, that a submarine's best defense is to stay undetected. And if detected, a submarine hopes to break contact as soon as possible and disappear once more. You can't kill what you can't find, and all that.

 

However, once firmly discovered, a submariner's life can become a frantic race for survival. (Many hours of Silent Hunter 3/4 have reinforced that point with me :lol: ). As with many other ASW technologies, the techniques and tools of evasion, decoys, and countermeasures have their origin in World War II.

 

1. Submarine Decoys and Countermeasures

 

From about 1942 onward, just as Germany beginning to lose its iron grip on the Battle of the Atlantic, the Kriegsmarine introduced the Pillenwerfer (or BOLD) decoy. This was a metal can or tube about four inches in diameter and filled with a alkaline metal (calcium or lithium) hydride. When released from a U-boat and exposed to seawater, a chemical reaction released large amounts of hydrogen that poured out of the container in thousands of gas bubbles and thereby, created a false sonar target. A hydrostatic valve held the device at a depth of about 100 feet, and permitted the effect to continue for about 20 to 25 minutes.

 

The principal limitation of Pillenwerfer, however, was that if an attacker could see both the stationary decoy and the moving submarine at the same time, it could differentiate between the two (the decoy lacking Doppler shift). Furthermore, the slow moving U-boats found it difficult to quietly slip away before the decoy expired.

 

A solution was found in a further German submarine decoy technology called Sieglinde. Powered by electric motors that allowed it to move at about 6 knots, as well as change depth, this decoy more accurately simulated a moving submarine. Used in combination with Pillenwerfer, this was a more effective method of allowing the real U-boat to escape.

 

In the post war period, the US Navy began work in earnest on developing a suite of submarine countermeasures, including acoustic intercept receivers which would automatically detect sonar signals, including the ping of actively homing torpedoes, over the full frequency range. Sonar jamming was also developed, much in the same way as electronic warfare is aimed against radars and radios, using both noise and deception (echo repeater) techniques. The most success has been obtained, however, in the field of expendable countermeasures.

 

In the modern era, a submarine facing an air dropped, acoustic homing torpedo has little opportunity to sneak away and must act quickly just to survive. An airborne lightweight torpedo may be dropped only a few hundred yards away, or less, and in many cases, will immediately go into active search and homing mode. Today's submarines are therefore typically equipped with a comprehensive expendable countermeasures system that combines both decoys (i.e. acoustic jammers) and mobile submarine/target simulators.

 

The decoys or jammers are ordinarily accommodated within their own individual launch tubes, and are ejected by compressed air, in either a manual or automatic (computer controlled) mode.

 

The US Navy's ADC (Acoustic Device Countermeasure) Mk 1, essentially an improved version of Pillenwerfer, was an expendable acoustic countermeasures device (an "ensonification bubbler") running on a saltwater battery, and weighing about 19 kg. It was introduced in the early 1970s. It has been followed by electronic decoys that actively emit an acoustic signal as a counter to homing torpedoes, beginning with the ADC Mk 2. These use a small, shrouded propeller to permit the decoy to "hover" in the water at a pre-selected depth. The Mk 2 has been followed (predictably) by the Mk 3, Mk 4, and Mk 5, which offer increasingly advanced signal generation. The British Royal Navy's submarine service, meanwhile, has used such decoys as the Type 2042 and Type 2066 Bandfish.

 

The Mk 57 Mobile Submarine Simulator (MOSS) is a 10 inch wide, mobile decoy that weighs about 1,000 lb and can only be launched through a torpedo tube rather than through a dedicated decoy launcher. Entering service in 1979, it was originally intended to protect ballistic missile submarines, with the Trident SSBNs carrying six decoys and the attack subs carrying four. And, because a MOSS might need to be launched at any time, one torpedo tube was usually kept empty and available. The MOSS has since been replaced by the six inch EX-10 Mobile Multi-function Device (MMD), which can be fired from a countermeasures tube. Soviet/Russian equivalents include the MG-74 and Berilly systems.

 

2. Surface Ship Decoys and Countermeasures

 

If an enemy submarine cannot be killed or avoided (including by such means as reducing one's acoustic signature, as with Prairie Masker described in Part 2), then for the surface ship it becomes a matter of torpedo defense. This can include maneuvers to complicate a submarine's fire control (such as the zig zag course taken by Allied convoys during WWII) and deployment of decoys and countermeasures.

 

The first of these was the British Foxer decoy of World War II, introduced in reply to the introduction by Germany's U-boat force of the G7es (T-5 Zaunkoning) homing torpedo in late 1943. There was nothing terribly sophisticated by Foxer. It was an arrangement of hollow metal pipes with holes cut into them, which was then towed about 500 feet behind a host Allied ship. To an early generation passive acoustic seeker, the noise produced by water rushing through the holes, and by the pipes banging together, made for a more attractive target than the ship's propellers.

 

The obvious disadvantage of Foxer, of course, was that constantly towing the decoy created more noise than might otherwise be produced by the ship (or the convoy it was escorting), thereby potentially attracting the attention of U-boats. After the war, the T.Mk 6 Fanfare was introduced, which more accurately simulated the noise of a ship's propeller rather than just produce broadband noise.

 

The most widely deployed towed torpedo decoy since that time has been the SLQ-25 Nixie (or variants thereof), which first entered service in 1974 and introduced improved deceptive countermeasures. The decoy or "fish", measuring about 37 inches long, six inches in diameter and weighing about 46 lb, is towed at the end of a 1,600 foot cable, and can receive the incoming torpedo's active sonar pings, amplify them, and then return the signals to the torpedo to lure it away from the ship. As with towed array sonars, it is generally unwise to tow the decoy at high speeds. Typically two SLQ-25 decoys are ready to be deployed (or "streamed"), in case one is destroyed by a successfully decoyed torpedo.

 

SLQ-25 Nixie torpedo countermeasures equipment aboard the USS Iowa (BB-61)

SLQ25_Nixie_Iowa.jpg

Image credit: US DoD.

 

Some torpedoes aren't easily decoyed by acoustic means - for example, the wake homers. For this reason, US Navy aircraft carriers can have a pipe lattice structure at their stern to produce a larger than normal wake: this reduces the effectiveness of torpedoes like the giant Russian Type 65 by forcing them to track back and forth across a much larger area, burning up valuable fuel (and thereby reducing their range) in the process.

 

Wake homing torpedo guidance

wake_homing.jpg

Image credit: US DoD

 

Other torpedo countermeasure programs have have sought to take advantage of the ubiquitous Mk 36 Super Rapid Blooming Offboard Chaff (SRBOC) launcher system fitted fleet wide in the US Navy, and widely exported to other NATO and allied navies. Ordinarily used to deploy chaff and infra-red decoys to defeat radar and anti-ship missiles, these 130mm launchers can now also use the Mk 13/14 Launched Expendable Acoustic Device (LEAD), a deploying a pattern of these decoys to seduce homing torpedoes.

 

3. The Hard Kill Option

 

In more recent years, navies have sought to develop a suite of integrated torpedo countermeasures that could automatically detect incoming torpedoes, deploy decoys or jammers to seduce or confuse them (the "soft kill" method), and if necessary, deploy anti-torpedo systems that could destroy them (the "hard kill" method). Examples of these efforts include the European SLAT (Systeme de Lutte Anti-Torpille) and the US-UK Surface Ship Torpedo Defense (SSTD) system.

 

The most difficult aspect of these kinds of programs has invariably been the hard kill element. One might wonder why it is tough to destroy an incoming torpedo. After all, we have developed the means to destroy supersonic sea skimming missiles, ballistic missiles, even satellites moving in orbit at 18,000 mph.

 

The answer: it is a fire control problem. Fire control depends on accurately predicting the position of an incoming weapon at the time of intercept by the defending projectile. That said, the detect to engage sequence for an underwater weapon is vastly more complex than that for airborne missiles. The ocean environment makes it significantly more difficult to receive and process data at a sufficiently high fidelity because of the speed at which information can be transferred underwater. Propagation speeds (radio frequency or infra-red signals in the air versus acoustic signals in the water) are nearly 200,000 times slower, so information is received significantly more slowly for a torpedo than for an airborne threat.

 

The development of an effective hard kill anti-torpedo system in the US Navy has been long and tortuous, evolving from the aforementioned US-UK SSTD program of late 1988 into what may eventually be achieved with the WSQ-11 Tripwire in fiscal year (FY) 2011. It is worthy of note, in comparison, that the Russian UDAV-1/RPK-5 Leevyen (Heavy Rain) or RBU-10000/12000, which combines a torpedo defense system of acoustic decoys, depth charges suspended by buoys, and explosives, has been around since 1989. The Israeli Scutter/Torbuster is another emerging system.

 

One unique system that has been under consideration came out of the DARPA Water Hammer mine countermeasures program in 2005. This would use explosives to generate a low frequency acoustic pulse in a sequence of shock tubes, which would in turn focus, amplify, and direct the pulse into the surrounding water over a narrow bearing, thereby creating a high pressure (around 2,000 psi) directional shock wave. This pulse could not only disrupt mines but would probably disrupt or destroy incoming torpedoes.

 

CONCLUSION

 

To quickly summarize, then, the ASW cycle requires detection of a submarine, location of its position, identification, targeting, and engagement. Its not at all as simple as that, of course, since each step in the process has its own quirks and is influenced by myriad factors, including the type of sensors at work, the nature of the target, and the tactics employed by both the hunter and the hunted.

 

In Part 4, we will conclude our discussion of ASW with a specific look at how it is simulated in Harpoon: Commander's Edition.

 

Source references:

U.S. Submarines Since 1945, Norman Friedman, 1994.

Jane's Navy International, November/December 1995.

Naval Institute Guide to World Naval Weapons Systems, 1997-98.

"What me worry? - The current state of surface ship torpedo defense". Vining, P. USNI Proceedings, 1999.

The Third Battle: Innovation in the US Navy's Silent Cold War Struggle with Soviet Submarines, Dr. Owen R. Cote Jr., March 2000.

Jane's Information Group: August 1999; June 2003; September 2005.

Journal of Electronic Defense, March 2001.

ASW after the Cold War, Owen Cote and Harvey Sapolsky, MIT Security Studies Program, April 2001.

Air Forces Monthly, May 2001; December 2003.

Proceedings, June 2002.

National Defense, January 2003.

World of Defence, UDT, Issue No.2, 2004.

U.S. Destroyers, Norman Friedman, 2004.

Navy Times, August 2005.

SOSUS: The "Secret Weapon" of Undersea Surveillance, Edward C. Whitman, Undersea Warfare, Winter 2005.

Principles of Naval Weapon Systems, Craig Payne, 2006.

Not Ready for Retirement: The Sonobuoy Approaches Age 65, Holler et al., Sea Technology, November 2006.

Harpoon 3 Sonar Model, AGSI, 2007.

Proceedings, June 2007.

ES310, Introduction to Naval Weapons Engineering.

Ocean Talk, Naval Meteorology and Oceanography Command.

Gyrodyne Helicopters.

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This is all going to got into a new Harpoon book, right?

 

I think we're going to skip the book and go straight to the feature film. :D

 

 

Thanks for these very informative articles. Is there any chance that they can be stickied on top of the forum or moved to their own section so that they don't get lost in the forum? I like to come back and read them every once in a while, but they get lost in all the other posts or moved to the second page, making them harder to find.

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Thanks for these very informative articles. Is there any chance that they can be stickied on top of the forum or moved to their own section so that they don't get lost in the forum? I like to come back and read them every once in a while, but they get lost in all the other posts or moved to the second page, making them harder to find.

 

Thank you. Its a lot of work, but I think the effort is worth it if we can build a foundation for game tactics (not just HCE, but ANW, H4 paper rules, etc), how the HCE code works, and where it can be improved.

 

I think its a good idea to "sticky" the articles. I'll look at doing that.

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  • 2 months later...
  • 2 weeks later...
that's interesting! thank you for sharing :)

simulation rachat de credit

 

Just read through all of the Shakedown series which were well written and very informative. Many thanks for taking the time to share this valuable information. Looking forward to the next one dealing with how it translates into Harpoon. Hopefully it'll help me with my less than stellar ASW prosecution. :)

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simple

 

If you see a sub coming, you better step aside. A lot of ships didn't; a lot of ships died. :P

 

 

Well done sir!

 

Its not a matter of bringing assets to bear but just simply having torps go "through" subs as shown by the animation (countermeasures?) or they never seem to close on the target even when dropping them nearly on top of the enemy sub.

 

I don't want to pollute Brad's good work here with a discussion of my failures though. Is there a better place to disucss newb questions/issues though?

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