Introduction
It has been one decade since the fall of the Soviet Union and the disappearance of the monolithic threat that drove United States force levels, strategies, and tactics for nearly 50 years. In the short period since then the U. S. Navy has redefined its role and shifted emphasis to influencing events on land from the sea. This requires access to the littoral waters of the world. Proliferating technologies are making safe access to this area increasingly difficult for the principal platform for power projection in the U. S. Navy, the carrier battle group. Three weapon technologies in particular are responsible for this, the missile, the modem sea mine, and the
submarine. Now, smaller nations that cannot afford conventional naval power (or even larger nations who simply don’t have the resources or technology) can disrupt the operations of larger navies operating in these coastal waters and prevent them from achieving their objective. The United States faces this possibility in several areas of interest, specifically the Korean peninsula, Taiwan, and the Arabian (Persian) Gulf. How might undersea warfare impact this situation? A scenario style study can be used to gain insight; here the Arabian Gulf will be used as the model.
Why the Arabian Gulf!
The Arabian Gulf is an excellent model for littoral warfare. It has a geographic chokepoint in the Straits of Hormuz, which are a mere 12 nm across at its narrowest point. It also happens to be the outlet for 20 percent of the world’s oil production, 1 making it important for western nations to keep open and extremely attractive for an adversary to close. Anti-ship missiles, sea mines, and
submarines are good weapons for access denial. Any U.S. battle group wishing to operate in the Gulf must pass through the Strait. The Gulf is shallow, its maximum depth being about 300 feet, and the waters are warm, with a high salinity and a high concentration of marine life. It also has a high shipping density. This is a poor acoustic environment. Reliable deep sound channels do not exist; it is predominantly an isothermal layer of water that traps sound between the surface and seafloor. While this sounds almost ideal it is anything but; the multiple reflections produce multiple returns for an active sonar system, making detection of targets and determination of range difficult, and multiple bottom interactions prevent accurate propagation loss predictions for passive sonar. The high shipping and high marine life levels produce higher ambient noise, further decreasing sonar performance. The increased density of marine life also produces higher attenuation and scattering, reducing the target information available.
The Arabian Gulf also features an excellent example of a littoral adversary: Iran. Iran has undertaken an expansion and modernization of its Navy in recent years. It is determined to be the pre-eminent naval power in the Gulf, and to control access through the Straits. 2 Iran also wishes to be able to make it difficult for adversary naval forces to operate in the Gulf and project power. 3 Iran is well positioned to control the Straits, with naval bases in the Arabian Gulf and outside on the Gulf of Oman. Iranian access denial capabilities have concentrated on submarines, missiles, and mines. The anti-ship missile threat posed by Iran is credible; it includes a possible 24 SS-N-22 Sunburn coastal defense missiles with eight launchers, several hundred CSSC·2 Silkworm coastal defense anti-ship missiles (ASMs), and an additional 100 CSSC-3 Seersucker AS Ms. 4 Iranian Thondor and Kaman class fast attack craft carry the Chinese built C-802 ASM, which was recently tested in the Unity-79 military exercise held in late October.’ The Sunburn flies at 3075 km/h and skims the surface at a mere 4.5 m as it flies toward its target, making it difficult to shoot down. 6 Combine these missiles with submarines and a mined Straits of Hormuz and passage into the Gulf becomes a challenge.
The Submarine Threat
Iran has three Russian-built Kilo (Type 877EKM) diesel submarines. This is a very capable submarine. It carries the Test- 71 ME and Test-96 wire guided torpedoes. The Test-71 ME is primarily an ASW weapon with active/passive homing, while the Test-96 is an ASW/ASuW (ASuW: anti-surface) weapon with active/passive sensors and wake homing. These Russian-built weapons have a range of about 8 run. 7 The Kilo has six torpedo tubes that have a rapid auto-reload capability; 18 torpedoes or 24 mines can be carried. 8 Its detection/attack capabilities are sup- ported by the MGK-400EM Shark Teeth hull-mounted low/medium frequency passive search sonar and the MG-519 Mouse Roar hull-mounted, high frequency, active search/attack sonar. The MVU-IIOEM combat system can track five targets simultaneously, two automatically and three manually. It has two diesel engines for driving on the surface and recharging batteries, which typically drive the 5,500 hp main motor. The Kilo also has a 130 hp economic speed motor for slow speed ( < 6 kts) operation in an ultra-quiet mode. Operational range is 6,000 nm when snorkeling at 7 kts and 400 nm when submerged at 3 kts. The Iranian Kilos may possibly carry the SA-N-10 SAM (surface to air missile) for defense against airborne threats. The first Kilo was delivered to the Iranians in 1992 and arrived with a Russian crew to provide training. The last Kilo was delivered in 1997; the second two did not come with Russian crews. The Iranians had some problems early on with the batteries due to the hot weather but corrected this with help from India who also operates Kilo submarines. 10 This led to some shortfalls in training and proficiency. Now all three are operational and operated together in the Unity-79 exercise, proving that Iran can sortie all three at once. 11 Their operational proficiency is rapidly improving. Many analysts in the past have underestimated the ability of a country that has recently acquired submarines to become proficient in their use, due to the large amount of expensive and experience necessary to run them. A historical analogy can help put this into perspective. On the eve of World War I Germany was the last nation involved to acquire submarines, they commissioned U-1 in 1906. 12 A mere eight years later Germany was able to sail these U- boats out into the North Atlantic and sink merchant shipping at will, without homing torpedoes. The Iranians should be considered proficient enough to surprise a modem warship with a wake homing torpedo. The Iranians operate their Kilos out of Bandar Abbas on the northern shore of the Straits of Honnuz. There are plans to move them to Chah Bahar on the Gulf of Oman. This planned base may have hardened bunkers to protect these assets while in pon. 13 It is obvious that the Iranians take these submarines very seriously, evidenced also by the money put into these vessels with little similar investment in their surface forces.
The Mine Threat
It is painfully obvious to any naval planner that the Straits of Hormuz are easy to mine. To anyone versed in mine warfare, they are also painful to clear. The poor acoustic conditions make it difficult to find mines, especially bottom mines. And once found, they have to be swept or cleared, actions that keep friendly forces within the range of anti-ship missiles. Also, the minefields could be patrolled by the Kilos as an additional hazard. Iran has an estimated 3,000 mines, including the Chinese built EM52 that lies on the bonom until activated, and then rockets to its target. 14 The Kilo can lay mines covenly. Once mined, any ship sunk in the Straits becomes a further hazard to navigation and will eventually block this vital passage itself. This is probably the most potent threat Iran has.
A Model for Countering the USW Threat
Any military planner who wishes to operate in the Arabian Gulf in the presence of these threats must plan how deal with them. In an article published in 1988, Jan Breemer proposed a “model” for conceptualizing alternative means for defeating the submarine menace. His historical frame of reference was the U-boats of WWI and WWII, but these ideas can be extended to today’s littoral USW threats, both submarines and mines. First, the war-making purpose(s) of the enemy’s undersea campaign must be identified. What is it he plans to accomplish by the use of submarines or mines? Then the question becomes one of how to defeat this purpose. For example, in World War II it was Germany’s intention to strangle Great Britain by sinking his merchant shipping. Therefore, any ASW effort by Great Britain should have been aimed at preventing Germany from accomplishing chis. The most effective means turned out to be The convoy system, which while it did not directly destroy the menace it did prevent Germany from achieving its submarine warfare purpose.
When confronting undersea threats there is a spectrum of options available. They fall into two categories: how to defeat the enemy’s purpose and where to do it. There are three basic options for each. His purpose can be defeated by destroying his ability, by containing this ability, or by limiting the effectiveness of his undersea methods (called blunting from here on.) These can be done at the source (such as the submarine’s home base), while he is transiting to his mission, or while he is engaged on that mission. 16 Some of the lines between locations are less distinct in littoral USW than they are in the open ocean. The matrix below summarizes this model.
Iran’s Undersea Purpose
Iran’s USW purpose can plausibly be inferred from the country’s overall naval aspirations. It wants to be the pre-eminent naval power in the Arabian Gulf and be able to control the flow of shipping through the Straits of Hormuz. 17 Submarines and mines serve this purpose: to deny access to larger naval forces seeking to operate in the Arabian Gulf or the Gulf of Oman. Success at doing so will prevent or at least make it very costly for a U.S. carrier battle group to operate in these littoral waters, and thereby possibly defeat U.S. war-making purposes. Conversely, it will be necessary for the United States to defeat the aim of the Iranian USW effort.
Destroying the Menace
The first option that most naval planners are likely to consider is destruction of the threat, and for good reason. It is the most final of all the methods, especially in the case where the enemy’s numbers are limited. Iran only has three Kilos and no indigenous production capability, so once those three submarines are destroyed there would be no recurrence of the problem. This is the case for many nations that the United States may have to face in the foreseeable future. Destroying the Kilos at the source is the most attractive, since it solves the first and most difficult problem associated with anti-submarine warfare, finding the submarine. The U.S. has proven in operation Desert Storm that it has the precision strike capability and intelligence assets to hit the submarines in their homeport of Bandar Abbas. This is the best option if it presents itself. This operation used to entail a great deal of risk when done by aircraft or surface units due to the typically heavy defenses around an opponents home base, but the land attack cruise missile changed that. The United Sates can now launch attacks against heavily defended bases with little risk. The key will be to send enough weapons to overwhelm the anti-air defenses around the submarines and allow them to reach and destroy their target. Due to the small number of targets the battle group commander will most likely have these resources at his disposal. One difficulty arises if the submarines are moved to Chah Bahar into what may be hardened submarine pens; 18 they won’t be as easily destroyed by U.S. Tomahawks, nor will it be as easy to ascertain if they are even there. The second problem is that this strategy assumes Iran has committed a strategic error and initiated hostilities without sortieing their Kilos . This should not be taken as a given. So while destroying the submarines at their base is the best option, the U.S. fleet commander cannot rely on the opportunity to do so before he is faced with the problem.
This same option, i.e. destroying the threat at the source, exists with mines, but is more difficult. One, they are easier to hide from intelligence assets. Two, they can be more readily distributed and protected from land-attack missiles and attack aircraft. Three, they also will most likely be deployed before the outbreak of hostilities, giving the fleet commander no time to destroy them before they are planted. If the opportunity exists, destroying Iran’s mining capability at the source solves the much more difficult task of having to find them in the water and dispose of them there. Again, however, the fleet commander can’t depend on this happening.
The second option is to destroy the threat while in transit. This is a little different in a littoral region than it would be in the open ocean. Transit should be considered to start once the submarine is underway from its homeport. Intelligence assets may notice that the submarine has left port, giving a warning to the fleet commander. If the carrier battle group is already on station, it can monitor the sub’s passage to some extent, depending on the location of assets. A submarine getting underway will use radar (that can be detected and identified) to make a safe passage out into open water, or it may be sighted (or picked up on radar) by units in the region while on the surface in water too shallow for submergence. This depends on having assets in a location able to pick up these indicators. Surface ships could be used, but these are vulnerable to shore or patrol craft based missile attack. Aircraft could also be used, but their endurance is more limited and they are also vulnerable to attack. The best platform for this would be a submarine, which could lurk in the area undetected waiting for the opposing submarine to come out. This is the best time to attack and engage an underway Kilo; it will make more noise while running on the surface using its diesel engines and it may be using radar. It may also be tracked visually. The problem with using the submarine is that it has to operate in water that is safe to dive in, thus giving the target an opportunity to also submerge before it can be detected. This is a function of how well trained the two opposing crews are; the more proficient crew will be more willing to operate a submarine in shallower water than the less proficient crew. It is also a function of ship size. Submarines maneuver better when they are shorter and wider. The Kilo has an advantage here over the Los Angeles class nuclear submarine used by the U. S. Navy, and may be able to operate in shallower water. Currently the Iranians seem to operate their Kilos in the deeper Gulf of Oman, 19 which may indicate that they are not yet comfortable operating in the shallow water of the Arabian Gulf and the Straits of Hormuz. If so, this should give U.S. forces some opportunity to locate them while transiting out. However, the Kilos proficiency will continue to improve so that crews will become more comfortable with sub-merging before leaving the Strait.
In that event, the target could then be prosecuted once he was underway and not under an umbrella of shore-based protection. Surface units have to be further away from the harbor choke point in order to stay out of missile range, or an assessment has to be made as to how survivable the surface unit is from any possible missile attack. In the Arabian Gulf this forces surface units to set up a line to the west inside the Gulf, the northern end of which may still be inside shore based missile range (which may be used to cover the Kilo’s transit), or they must set up to the east of the Straits out in the Gulf of Oman, depending on where the Kilo is going. This would be a wider area to cover for which the commander may not have the assets and will give the Kilo time to
submerge, at which time the poor acoustic conditions will hide it well. The problem only gets worse as the area that needs searching becomes larger. Once the Kilo has moved out of port and sub-merged, it will not have to surface again, since it can snorkel to recharge its batteries. Now, the battle group commander needs the Kilo to make a mistake, for example, having the snorkel mast detected by a search-radar or creating enough noise that it can be heard. Due to geography, the Kilo may not even have to snorkel before reaching its target, robbing the battle group of a valuable opportunity to detect it. If operated with skill, it is unlikely that the battle group will be able to relocate the Kilo until it reaches its target.
Another possible method of detecting submarines as they leave port is to place sensors outside harbors and road steads. The United States is working on this in the form of the Advanced Deployable System (ADS), a system of transportable acoustic sensors that could be placed in the area of interest prior to the outbreak of hostilities or the arrival of the battle group. The U.S. Navy plans for initial production to commence sometime this decade. 20 These kinds of sensors can provide the cuing needed to shrink the area that surface, air, and subsurface units need to search and free up units that would otherwise be tied up in surveillance. It gives the fleet commander more flexibility with his limited resources. Once ~e Kilo is detected underway, the battle group could send assets to prosecute it. It would still be a difficult task, and success would depend on the proximity of the attacking units and on the ability of the cueing system to send timely data to the battle group. This method also points to another way of destroying the submarine in transit, namely by mining his homeport. This also reduces the number of assets required to maintain a vigil on the port, but does not eliminate the need for them entirely. An un-patrolled minefield will be cleared and allow safe passage of the enemy submarine. Another submarine is the ideal platform for mining the harbor covertly and patrolling it once the minefield is laid. The shallow water depth may prevent the submarine from placing the mines as close as desired, however.
Mining and then patrolling the harbor again assumes that Iran failed to get their boats to sea prior to initiating hostilities. This scenario is unlikely and will most likely not be a solution available to the fleet commander.
The last opportunity to destroy the enemy submarine occurs while it is engaged in its purpose, attacking the battle group or merchant shipping. This makes the enemy submarine easier to find since the area that needs searching is smaller than when it is in transit. It also allows the battle group commander to keep his limited assets close to the carrier where they are needed for other roles such as air and missile defense. The Kilo will still be difficult to find and will be on its best behavior while getting into position for attack, it cannot be depended upon to make any revealing mistake at this stage. The Kilo also carries weapons that make its standoff range considerable; it could launch wake homing torpedoes from as far away as 5-8 nm if it can detect and track the target from that range. The Kilo is completely capable of making an acoustic attack on a large warship since it will hear the ship before the ship can detect the submarine. Active sonar from surface units will do little more than give the Kilo targeting information; they will probably not find it before it can attack. The Kilo’s six torpedo tubes provide for a large salvo ability and the ability to rapidly reload them makes it hazardous for a surface ship to approach the submarine’s position. At this point an aircraft is probably the best means to attack an exposed submarine threat. Surface units that carry the Mk 50 torpedo have a weapon with good shallow water capabilities and a high probability of target kill, but the Mk 50’s range is roughly equivalent to or inside that of the Test-96 wake homing torpedo carried by the Kilo. This makes it unsafe for a surface unit alone to prosecute a Kilo submarine.
Submarines could also be used here; they are still the most effective acoustic sensor and weapons system available to kill another submarine. There are two issues here, acoustic advantage and ASW proficiency. The submarine with acoustic advantage will get to shoot first. It is difficult to tell which submarine will have it since both a Kilo and a Los Angeles class submarine are both very quiet targets. And no matter which submarine has it, the ranges are likely to be fairly small and now the effects from an own ship’s weapon become important, as well as counter-fire from the opposing submarine. The Los Angeles submarine has an advantage in submerged speed and is more capable of evading a weapon than the Kilo is. The Los Angeles class could make up for lack of a positive acoustic advantage by using active sonar and depend on evasive maneuvers to keep itself out of trouble. This is very risky not only because it gives the opposing Kilo a better chance to fire but also may not help to find the Kilo in the poor acoustic conditions. A long-standing difficulty in using submarines to directly protect the battle group concerns communicating with and coordinating the submarine’s efforts. A submarine generally has to be at periscope depth to communicate and receive cuing information from other sources; this limits the submarine’s maneuverability. However, due to the surface duct narure of the acoustic environment, this should not degrade its sensor performance as much as it normally would in deep water. Despite the poor acoustic conditions of this littoral region, there is generally no strong layer that a submarine can hide beneath. This is not always true; very low sea states and high temperarures during the daytime can create a surface layer of warm water from 30-45 ft deep which will have some effect on the acoustic performance of a submarine’s sonar. 21 There is also a marked difference between day and night biological concentrations, making ambient noise levels near the surface higher at night and degrading sonar performance. The submarine could stay in contact with the battle group, using its own sensors to search the area, and be available to send a threat warning to the battle group commander or receive target information that will allow the submarine to go prosecute a submerged contact.
Another detection method being considered is low frequency ( < 1 kHz) active towed sonar systems. These systems could be deployed off surface units that screen the carrier and used in a traditional mono-static (source and receiver the same) or multi-static (source and receiver are physically separated) configuration with other units. This option is being investigated by the Office of Naval Research (ONR) and shows some promise. However, due to the long wavelength false target detection rates could be fairly high. Prosecution and destruction of the submarine in close proximity to the enemy submarine's objective requires a concentrated, coordinated effon on the pan of the battle group. It becomes more important than ever for all platforms to be able to share data and a common tactical picture. Destroying mines in this phase of the scenario is nothing more than traditional mine hunting. As stated before, poor local acoustic conditions make this difficult. It is also time consuming. Since the most likely area to be mined is the Straits of Hormuz, traditional mine-clearance forces will be subject to shore-based missile attack. The minefield is also likely to be patrolled by fast patrol craft armed with anti-ship missiles, or Kilos. Thus, destruction of the enemy's missiles and patrol forces is needed; it may also be necessary to destroy the Kilos prior to sending in traditional mine counter-measures forces. The perfect mine hunting and clearance platform may be a submarine. They are not vulnerable to missile attack and have a better chance of defending themselves against any Kilos patrolling the minefield, if detected at all . This will require some development of mine detection and localization capability aboard the submarine. The safest method lies in the development of urunanned undersea vehicles that can swim out and localize the mines, then rerum to the submarine. The U.S. Navy has a Near- term Mine Reconnaissance System (NMRS) UUV than can be deployed and retrieved through a torpedo tube and can be used to search out minefields. The Navy is also working on the follow on Long-term Mine Reconnaissance System (LMRS) UUV, expected to be operational in 2003. 23 Once the mines are detected, the submarine could deploy divers to destroy the mines, though this would require decompression ability onboard the submarine.
Containing the Threat
The mine threat can be contained by destruction of the Kilos, thus eliminating any coven method of deploying mines, and next by establishing air and sea superiority to prevent other forces from deploying mines. This assumes that mines have not been planted yet and the United States has the strategic initiative. Otherwise, contairunent of the mine threat is not possible.
Contairunent of the enemy submarine starts with the threat of destruction. The Kilos could be contained at the source by a naval presence off their home base, but this would subject those forces to missile attack until the opposition’s missile capability can be destroyed. Doing so also ties up forces that may be needed elsewhere. Submarines can also be used to contain the Kilos in pon. The submarines may have to be a semi-oven presence, which may require the occasional use of active sonar or the destruction of another unit. Keeping containment leak-proof is probably impossible, for the same reasons it is difficult to destroy the Kilo while it is in transit out of port. It does bring up a slightly different method of contairunent, which is to shadow the threat submarine as it leaves homeport, and be ready to destroy it at some point or to report its movements to the battle group so they can take early defensive action. This is difficult due to poor acoustic conditions; it also takes one submarine per Kilo to carry out. The battle group commander may not have these assets available. This strategy is more acceptable if hostilities are imminent but not started, so the fleet commander can monitor the Kilos as a precautionary measure. The off-board sensors described earlier are especially useful in this case. They could be placed well in advance of anticipated hostilities and provide warning of the Kilos movements, which could be a pre-cursor to hostilities. The battle group commander could then dispatch units to intercept the Kilo and ready his forces for a possible attack. A minefield laid around their homepon could also contain the threat submarines. As in the destruction case, these minefields would have to be patrolled to be effective.
Limiting the Threat’s Effectiyeuess (Blunting)
The enemy’s USW effectiveness can be blunted while his submarine is transiting to its patrol area or while it is engaged in attacking. While in transit, it can be harassed by air patrols, which may make it more risky and more difficult to expose its snorkel mast, and by surface or submarine patrols using active sonar. This may force the enemy submarine to take a longer, more circuitous route to its original target to avoid possible detection. This method requires either an ability to keep track of the submarine’s movements (in which case it could probably be attacked) or numerous forces to increase the likelihood of intercepting it. While this does expose those forces to an attack by the Kilo, such an event would surrender the submarine’s element of surprise in pursuit of its desired target, the battle group itself. This is not a preferred method of dealing with the Kilo but may have to be used to protect higher value units. The Kilo will not be able to achieve its war making purpose of preventing U.S. forces from projecting power if it does not get an opportunity to attack the carrier. This is the basic idea behind surface escorts screening the carrier from ASW threats. In this case the objective must be to keep the Kilo out of weapons range of the carrier, this is about 8-10 run with existing weapons.
There are two other methods of blunting the Kilos war-making purpose. The first is trivial in terms of undersea warfare capability; eliminate the need to operate in the littoral areas. Since this is not yet a possibility it will not be discussed here. The second is to find some method to make submarine attacks less effective. This is the idea of torpedo defense, or the ability to destroy an incoming torpedo before it gets within range to damage its target. This is being worked on by many of the world’s navies but is not yet a reality. Some of the problems are in detection of the torpedo, especially in the poor acoustic environment of the Arabian Gulf, targeting the torpedo, and then launching a weapon that can intercept the torpedo. 24 The best options currently available are evasive maneuvers and torpedo decoys; these tend to be ineffective against wake homing weapons.
Conclusion
For now and the foreseeable future the U.S. Navy will be the world’s largest and best. Most nations will not be able to challenge that supremacy and will seek to undermine it by making it risky for the United States to deploy its power projection assets in the littoral regions of the world where they are most effective. The best assets available to these nations will be quiet diesel submarines, sea mines, and effective anti-ship missiles. As can be seen by the example Iran provides, this is exactly what these nations are procuring. We need to devise strategies, tactics, and technologies to deal with these threats or risk watching our most powerful assets sit outside the areas they are most needed or be lost trying to enter them.
