Because of their inherent capability for stealth and surprise, submarines are the most deadly adversary faced by modern naval commanders. Until recently, the bulk of U.S. ASW doctrine focused on countering a Soviet submarine threat out of the Norwegian Sea and the G.I.U.K. gap intended to interdict the sea lines of communication (SLOC) in support of a ground war in Europe. With the dissolution of the Soviet Union, this possibility has virtually evaporated. In its place, however, looms a broader, potentially more devastating threat.

With the loss of an obvious challenger for open ocean supremacy, and a political climate emphasizing budget reduction, the U.S. maritime structure is being incessantly whittled away. Further, the naval hierarchy is shifting mission emphasis away from strategic control of the oceans to support of joint operations in coastal conflicts. In this capacity, the blue-water turned brown-water navy is viewed as a method of quick power projection ashore, via air and missile strikes as well as amphibious ground forces. Astute naval commanders are aware that, in order for power projection operations to be undertaken with an acceptable degree of risk, sea control of the objective area must first be obtained. Therein lurks the new danger.

The CIS is strapped for cash and its most readily available export commodity is hardware from its once-mighty military machine. Although their arms sales efforts have already extended to all platform types short of nuclear weapons, we will focus exclusively on their support of submarine proliferation. Most notable amongst current negotiations are the purchase of several Kilo submarines by Iran. These boats represent some of the most advanced diesel electric technology in the world, which gives thema very quiet acoustic signature. One need not be a military analyst to appreciate how the presence of such platforms would complicate naval operations in any future Gulf conflict. Additionally, Libya, Syria, and Algeria, all of whom already operate Soviet submarine designs, may obtain additional modern boats.

When you add these developments to the fact that shallow-water ASW is the most difficult type of ASW to conduct, one develops an appreciation for how any new maritime strategy must place additional emphasis on this warfare area. In the remainder of this section, you will find detailed briefings on the impact of oceanographic conditions on tactics, area vs. local ASW, how to assess your own force’s capabilities, and other topics of vital importance to battlefield survival.

Sound propagation in the ocean is affected by temperature, pressure, and salinity. Of these, temperature is the dominant characteristic. The ocean temperature varies greatly with depth, but somewhere between 100 and 300 feet there is usually an abrupt change between the relatively warm surface waters and the cold, still depths beneath. This rapid change in temperature is known as the thermocline, or sometimes ‘the layer’. Beneath the layer the water temperature tends to be isothermic, or relatively constant. The layer is tactically significant for several reasons. First and foremost, sound emanating from a source on one side of the layer (either above or below) tends to remain trapped on that side of the layer. Simply put, the sudden change in water temperature causes sound waves to bounce back from the layer. It is not an impenetrable barrier; there is some leakage, particularly with very high frequency noises like cavitation (the effect where bubbles produced around propellers collapse noisily in the wake) and active sonar transmissions. A general rule of thumb however, is that most noises will be greatly attenuated (reduced) if they must pass through the layer. You will therefore hear noises made on your side of the layer much easier than those emanating through it.

In reality, layer depth varies from location to location and submarines try and stay comfortably beneath it to help hide from surface ships. In Harpoon Il, the thermocline always defines the boundary between the Shallow and Intermediate depth bands.

Commanders must constantly assess whether their sonar emissions policy should be active or passive, based on the tactical situation. To understand the basics, it is important to first illustrate the influence of the layer in a generic encounter between a surface ship (Blue) and a submarine (Orange). In the first case, (Figure 6) Blue is operating at 5 knots towing a passive sonar array above the layer. Orange is also operating at 5 knots below the layer. Note that the sound waves emitted from both platforms are minimal, so only those crossing the layer at an acute angle (e.g.. straight down or up) will penetrate, while the bulk of the sounds will be reflected or refracted. Those sound waves that do penetrate directly through the layer form a narrow cone of sound. In this case for either Blue or Orange to detect the other, they must physically pass through the direct path cone, which means they would virtually be on top of one another, and detection would be almost simultaneous.


Figure 6: The effect of the layeron sonardetection.

In our second example, (Figure 7) Blue is towing his passive sonar array below the layer. All other conditions remain the same. Blue is now be able to directly receive any sound waves emitted by Orange, which means that he would detect Orange at a considerably farther range, while remaining undetected himself. The actual detection ranges will vary with the amount of noise emitted by Orange, as well as the sensitivity of Blue sonar suite. Base noise levels will also differ from platform to platform (some subs are quieter than others) and will be increased by noisy activities such as moving quickly or firing weapons.


Figure 7: The effect of a towed array below the layer.

In our third example we'll look at how Convergence Zones (CZ) work. As you go down into the ocean depths, the pressure steadily increases. This change in pressure also equates to a change in the speed of sound, which rises as the water becomes more dense. Different depths end up having a different speed of sound. Sound waves which travel down into these depths are bent by this effect and slowly refracted back towards the surface in a long sweeping curve, surfacing many miles away. If conditions are right, these sounds will bounce off the surface and start back down into the deeps again on another long curve. The locations where these sounds reappear near the surface is called the convergence zone. CZs occur about every 66,000 yards (33nm), centered on the location where the sounds originated. They form an annular pattern of concentric circles around a noise source. Sounds traveling on a direct path from A to B might fade out relatively quickly (after a few miles perhaps), but sounds caught in a convergence zone might propagate for over a hundred miles with much less attenuation. Sensitive sonars capable of recognizing CZ signals are very important sources of tactical information. The picture in figure 8 shows a Blue surface ship using its active sonar. Modern active sonar transmissions are extremely powerful (about 250 dB) and are capable of literally boiling the seawater surrounding the transducer. Power outputs any higher than this are useless because boiling seawater makes for a lousy conductor of sound. Generating this much noise in the water makes this ship counter-detectable at ten times its own range. As such, Blue is considered to have surrendered the initiative to any subsurface threat within 100nm, as his transmissions act like a giant homing beacon.


Figure 8: The effect of a hull-mounted active sonar.

Blue will get reflections (detections) from his active sonar out to about twenty miles. The submarine in this figure is hiding beneath the layer however, and is still relatively safe from the bulk of Blue’s active sonar signal (which is bouncing harmlessly off the layer). Some of Blue’s sound energy will penetrate through layer and travel down into the deep sound channel. There it curves back towards the surface and reflected down once again. Eventually, some of the noise that Blue is making finds its way to the surface ship in the second CZ While Blue is deaf to anything but the short range echoes of his active sonar, the possibility exists that this other surface ship will hear him from many miles away.

Note that some of Blue's sonar energy does penetrate the layer at an angle which might allow for a direct path detection, were the submarine close enough. In this case however, the angle of incidence is not enough, and the submarine will escape detection, so long as he stays away. Active sonar is good for immediately localizing a near target, especially one on the same side of the layer with you. For more information on how Harpoon Il models sonar and convergence zones, see the technical notes at the end of your manual.

Let us consider now another case, where Blue possesses a variable depth sonar (VDS) in conjunction with his towed array. By putting the combination of active and passive capability on the same side of the layer as Orange, Blue can listen for Orange as before, but as soon as he feels Orange is within striking distance, he may selectively go active for one or two transmissions from the VDS and obtain an immediate targeting solution on Orange. The range at which a return echo is strong enough to provide this solution is again variable, depending on the type of sonar, the aspect of the target, the presence or absence of anechoic coatings, and numerous other factors. While listening below the layer as noted above, the hull mounted sonar is still capable of passive or active operations above the layer. This configuration is optimum for the conduct of bluewater ASW.

Earlier, it was indicated that shallow water operations are the most difficult to conduct. It is now important to explain why. In the examples just presented, you may have noted that, as a rule, passive detection ranges far exceed active ranges. When an active contact is held, both parties are usually within striking distance of one another. Naturally, the commander would prefer to expand his battle space and engage the enemy before he gets within striking distance. As such, passive operations are the norm in most cases. Shallow water operations are an exception to this rule.

Although biological noise sources are present throughout the ocean, and are frequent sources of false contacts (i.e.: whale blowing sounds like ballast tanks being blown), the highest concentration of biological activity is in shallow water. Further, wave and tidal action, the influx of rivers and estuaries, and other natural phenomena combine to make passive ASW virtually impossible for either side, although submarine sonar operators are a little more adept at sorting out background noises than their surface counterparts.

The second factor to consider is that shallow waters have a minimal thermal gradient and none of the aforementioned layer of CZ effects. As such, both surface and subsurface units are always on the same side of the layer. Although no sub commander would ever surrender his only advantage (stealth) by using active transmissions to search for contacts, surface forces are virtually required to use active sonar whenever a shallow water submarine threat exists. Again, while this must be done with counter-detection ranges in mind, the task force commander obviously must have some other reason to sacrifice strategic mobility and operate close ashore. Therefore he must assume he is already detected, if not targeted. Given that, the logical choice is to adopt the best defensive posture for the force and hope his surface search radars pick up any periscopes from lurkers setting up a shot. What we have not explored up to this point, however, are the measures he may have taken to minimize that threat during his transit to the area of operations.

For a theater level ASW campaign to be successful, the commander must correctly employ all available ASW assets: surface, air, and subsurface. Each component of the ASW triad has strengths and weaknesses that must be clearly understood for proper tactical use.

Of the three, submarines are the most effective at finding and killing other submarines. The root of their strength lies in stealth as well. A low self noise means they can hear sound just as well as their prey. Because submarines can best accomplish this mission area as solo players, the use of SSNs as Hunter-Killers will be discussed separately, in the section below entitled “Commanding a Submarine”. Here we will focus on the interplay of surface and air assets attempting to detect, localize, and target submarines in a layered defense. These phases of an engagement are analogous to the aforementioned qualities of passive cross fixes, and understanding their meaning is critical to subsequent discussion:

Area ASW has several applications, but the specific platforms and tactics used to conduct it remain constant throughout the range of applications. The platforms of choice are maritime patrol aircraft (MPA), like the P-3 Orion, and towed array equipped surface ships, because each possesses endurance and potency, in terms of weapons load. SSNs also conduct area ASW, but, again, their use will be explored later. Of the two, towed array assets cover a greater area, but require more time to do so, while MPA assets cover more area per unit of time, providing a quicker search of a smaller area. An alternative choice for area ASW are CV-based aircraft. Although they have a shorter endurance and lighter weapons and sonobuoy loads, they make up for it by being close to the action and having shorter transit times.

Area ASW is the coordination of search efforts ahead of the main force on specific areas of ocean holding tactical significance. The objective of Area ASW is to detect and localize any submarines within the area as a minimum, and to destroy them should the tactical situation and rules of engagement allow. Within the concept of layered defense, area ASW provides the first opportunity for a commander to attrit enemy submarines.

Examples of area ASW would be the sanitization of chokepoints, such as straits and narrows, by a ship equipped with a towed array operating 30-50nm ahead of a task force along the PIM. Also, a task force required to transit at high speed is less vulnerable to subs closing in from behind the force, but much more vulnerable to subs laying ahead and to the sides of the PIM. These task forces may use patrols of MPA assets 150nm in advance of the force and on either side for the duration of the transit.

In the conduct of area ASW in Harpoon Il, the commander may specify the area of interest for the MPA asset to prosecute by laying out a patrol area bounded by reference points.

Once submarines have penetrated past the units conducting area ASW, their next obstacle to overcome would be the outer screen. As was discussed briefly in the section on unit positioning, outer screen assets should consist of ASW and AAW platforms, to allow for mutual defense in conjunction with their picket duties. Assets of the outer screen should be passive and conducting search operations above and below the layer.

Because of their separation from the main force (12-24nm with a preference for even more distance), any contacts generated by units of the outer screen will generally pose an immediate threat only to those units and not to the main body. Cruise-missile-equipped submarines may be an exception to this rule; though if the main body stays in strict EMCON Alpha (no betraying emissions), it is likely the submarine does not have enough information to fire on them. Still, prudent commanders will turn the main body away from the contact while the screening units attempt to prosecute it.

Screening units should jump all over the submarine contact with helicopters. With at least two ships and a helicopter holding passive contact, the targeting solution should come rapidly enough to conduct atorpedo attack with aerial delivered weapons. A stand-off weapon, such as an ASROC, may be used if the submarine is in too close. Alternately, if the passive contact is of sufficient strength that the on-scene commander believes the submarine is within his active envelope, then he may elect to go active with the sonar and conduct an immediate over-the-side shot. Whether this attack is effective or not (and it generally is one of the least effective methods), it does succeed in putting the submarine on the defensive, buying the commander time for a more thorough follow-up attack.

The tactic just discussed is also the tactic of choice should a submarine be fortunate enough to penetrate to the inner screen. Because it has already achieved firing position on the HVU of the force, any and all efforts must be made to distract that submarine from attacking. Time is of the essence in getting weapons in the water, even if they are not accurately targeted. Concurrent with these attacks, the commander must execute all appropriate torpedo evasion maneuvers based upon his knowledge of the loadout carried by the class of submarine contacted.

The scenario of a prowling submarine inside the boundaries of a formation is the nightmare of every task force commander. As such, there has evolved a body of doctrine that may be selectively employed by the Harpoon Il commander to complicate enemy efforts to achieve this position. Obviously, all of the considerations relative to EMCON posture and counter-targeting still apply, but the commander may also decide to invoke a zig-zag plan. A submarine commander may not wish to risk sticking a periscope out of the water or using active sonar, so he must perform a passive Target Motion Analysis (TMA). Simply put, a submarine commander will determine the course and speed of his targets by observing them passively and calculating relative motions from the bearing changes he sees. Since passive sonar consistently gives a direction to a target, but no other information, the submarine must perform this TMA on targets for several minutes before they are certain of their information. If the target suddenly decides to zig-zag, all this careful work goes right out the window and the submarine must start all over again. Once the submarine commander has a working solution on his targets however, he may fire modern homing torpedoes or missiles. This targeting solution is what the task force commander is trying to deny the submarine commander.

Harpoon II does not include any preset zig-zag plans, but the user can easily create them via the navigational plotter. Occasionally introducing a zig-zag in your group’s course will further complicate any submarines attack against you.

Submarines pose the greatest sustained threat in the multi-threat environment. Commanders must consider their ASW posture as an integral part of all mission planning. To successfully prosecute submarines, one must have an understanding of the tactical elements of the environment they operate in, and use every ASW asset at hand to counter their inherent advantages of stealth and surprise.

“The San Luis was at sea, and at times in the area of the British force, for an estimated 36 days. The threat from the Argentine submarine was a continuous concern for the British Task force commander, and numerous attacks were made against suspected submarine contacts, with a large number of ASW weapons being expended. In any event, San Luis survived all British ASW efforts.”

-From the briefing prepared for the Secretary of the Navy, The South Atlantic Conflict Lessons Learned

What the Harpoon II commander should garner from this observation on the Falklands War is not only that ASW is difficult, which should already be internalized, but that a single undetected submarine can complicate the battle plans of the adversary considerably. Also, similar to mine warfare, the suspicion of the threat is sufficient to force the commander to commit large numbers of resources to eradicating it, resources which would otherwise be available to support his primary mission.

Thus far, the focus of this guide has been on countering the submarine threat to your own force. In this section, we will reverse tack and become the threat. By learning the optimum employment of submarines from a commander’s perspective, one will not only possess a potent new force multiplier, one will also gain further insight into how enemies will attempt to use this platform to advantage.

The first major leap of faith required of those who will muster subs on the battlefield is that they cannot be micro-managed to the degree that other forces permit. Although earlier releases of Harpoon allowed the commander to issue orders to submarines whenever the mood struck, this is inconsistent with real-world constraints. For submarines to be in constant communications, they would have to remain at periscope depth all of the time with their communications mast raised. Naturally, such a posture would eliminate virtually all of the tactical advantages a submarine possesses. The trade off with stealth is not being aware of the sub's activities at all times. The most important thing to understand is that , in the case of missions with extended durations, the commander will not know for certain until the battle is over if the sub is still active; the only indication will be the loss of contact. After the scenario ends, the tote board of casualties will be updated to reflect actual losses of friendly submarines.

In some instances, a commander will have a submarine in direct support of a task force (SSNDS). This asset is usually stationed in a distant sector on the formation editor as an ASW barrier patrol. Because of special communications gear contained in the active sonar suites of surface ships, submarines operating directly with the battle group may be alerted to come to communications depth at any time. Again, if the submarine skipper is not in contact with an enemy sub (which would now be alerted to the presence of the friendly, if not its precise location), he will come to periscope depth for communication. There is a delay based on the actual time it takes to change depths, but, once the sub is there, the commander may alter ROE, mission tasking and movement orders as above. One other tactical tip before moving on - because the special sonar transmission used to call SSNDS assets to the surface is recognizable to the enemy, it is sometimes beneficial for a commander without an SSNDS asset to radiate it anyway, making any enemy subs in the area think another sub is present.

Excluding SSNDS, most missions assigned to submarines reflect their ability to operate independently and respect their ability to strike effectively without additional guidance. As such, the prudent commander will consider the need for stealth and surprise and capitalize upon the strengths of submarines in mission planning without placing them in unwarranted risk.

Prior to the commencement of hostilities, submarines are the platform of choice to conduct reconnaissance of enemy strength and disposition, as well as conduct offensive operations like the mining of enemy sortie routes. From this inshore position, these same submarines can act as linebackers for their minefields, conducting follow-up attacks on enemy assets transiting the area. Also, if missile equipped, these same submarines can either conduct preemptive strikes on enemy airfields or ports or lay in wait to strike in conjunction with air elements of the main task force.

Additionally, when the enemy has limited ASW capability, as is the case with many coastal nations, a submarine may be positioned close ashore with its periscope raised to report the movements of enemy air groups coming offshore against the main force. This is a new method of passive airborne early warning that has been used with success by Sixth Fleet assets in the Mediterranean. Also, as a scout, submarines can provide ESM cross fixes and visual surface searches from their area of operations. The latter can be critical in monitoring traffic through congested areas like straits and narrows and identifying contacts of interest to preclude fire on neutrals. Finally, submarines are also capable of performing battle damage assessment when used in conjunction with other forces in a joint attack.

With hostilities in progress, submarines may be used in their traditional role of Hunter-Killers. Submarines are the most effective platforms at locating and destroying enemy submarines, so they should be considered for all area ASW plans. Do not discount the diesel boat in this equation either. The Batfish located and destroyed 3 of 4 J apanese submarines operating around the Philippines in as many days in WWII. Modern diesel boats are much more capable than their predecessors and are a match for the most capable SSNs if handled properly. Also as Hunter-Killers, submarines may seek and destroy enemy warships or cripple the war effort of the adversary by pursuing a Guerre de Course. A commerce war on merchants and auxiliaries is a great fear of western nations, as these assets are in much shorter supply than during WWII, when ♥♥♥♥ U-boats almost succeeded in breaking the Allied back in the North Atlantic.

“If we would have had more U-boats, we would have won the war!”

-Admiral Doenitz, Commander of the German submarine forces in WWII from his book, The Modern Diesel Boat

Though some analysts would point to Germany’s Type 209 diesel boat as an example of modern technology, this very quiet submarine still requires six hours of snorkel time to charge, is limited to about 100 meters depth and must patrol at 1-2 knots to retain its stealth advantage. The Russian Kilo design, on the other hand, is capable of going without snorkeling for as many as 2-3 days at a 2-3 knot patrol speed. As such, it is a much more capable adversary.

Despite the ability of the diesel boat to be a devastating threat, U.S. analysts discount their effectiveness in the hands of third world crews due to a lack of training. Whether these assumptions would prove out in the real world or not remains to be seen, but the Harpoon Il commander can learn from the reasoning behind this assumption and employ the antithesis to make his diesel forces stronger.

The presumption is that these crews will expose their masts much more than necessary, because they do not know how to conduct a passive plot correctly. Further, there is a great deal of skepticism that they are capable of making a deep submerged approach on batteries, the most advantageous tactic, because of a constant need to refine their position estimates in relation to the target. It is also assumed that diesels resting on the bottom would snorkel at least once a day to preserve the amount of battery power they would need to escape after an attack. This line of reasoning reflects a dangerous tactical arrogance. Whether or not these potential adversaries are currently capable or not, they could become so in short order under the right circumstances. The prudent commander can never discount this threat on the presumption that it will be improperly employed.

If used properly, with forethought and patience, the commander of submarine units possesses a powerful force multiplier. Further, in the correct tactical placement, submarines can contribute to all of the warfare mission areas, including Strike, AAW, and EW, not just ASW and ASuW as in the past.