[A recent visitor al w MTI’ DACS program, OCttJIIDfl’tlpMr E~ne Mwnikov is a Doctor of Physics and membn- of the Moscow Instilule of Physics and Technology’s Centn- for .Anns Contro~ Energy and Envirorumntol Studies.]
On February 11, 1992, while operating in or near Russian territorial waters off the port of Murmansk, the U.S. attack submarine USS BATON ROUGE was struck from behind by a Russian SIERRA class submarine. Although such collisions have occurred in the past, this one has generated more atten-tion. Contradictory press accounts of the collision, published in both the U.S. and Russia, raise two questions: What was the U .S. submarine doing so close to the Murmansk naval facilities? And how could such a collision have occurred?
These two seemingly simple questions, however, raise a third question that points to issues of prime importance for security planning in both Russia and the U.S: Does this collision tell us anything important about the capabilities of U.S. submarines to conduct anti-submarine operations against the newest genera-tion Russian submarines? If so, could this incident indicate that current and future generations of Russian ballistic missile submarines could be held at risk by U.S. Navy undersea forces? Here I examine these questions using both Russian and American sources as well as a technical review of the capabili-ties and limitations of submarine sensors in shallow coastal waters. In particular, our analysis indicates that in the shallow northern seas, even under the best environmental conditions, the technical capabilities of modem covertly operating subma-rines do not allow the detection of other modem covert submarines at distances of more than a couple of hundred meters.
What Do We Know About the Incident?
The USS BATON ROUGE, a LOS ANGELES class nuclear attack submarine and the Russian SIERRA class submarine collided at 20:16 Moscow time, at 69°38.7′ North and 33°46.9′ East, roughly 4. 7 miles from the line connecting Tsypnavolok Cape and Kildin Island (see Figure 1.) The U.S. Navy stated that the collision occurred more than 12 miles from the shore, at a location in international waters. However, Russia uses a different set of rules for defining the boundary between territorial and international waters,1 and the Russian rules put the collision site inside territorial waters.
The dispute over exactly what areas of coastal ocean can be considered international waters is important since international coastal waters can be used for a wide range of activities and many questions of rights and rules of the road are effected by whether or not naval operations occur within territorial or international waters. In the particular case of Murmansk — the largest base of the Northern Fleet — there are obvious addition-al concerns about the security and operation of Russian warships near their home port.
According to U.S. officials, the collision occurred when the SIERRA was surfacing beneath the BATON ROUGE, which was at a periscope depth of 22 yards. U.S. reconnaissance photos of the SIERRA reportedly showed a large dent in the front section of her sail structure and indicate that the Russian submarine’s sail may have hit the underneath aft section of the BATON ROUGE. According to Soviet reports, the SIERRA incurred slight damage to her sail, where substantial bits of the U.S. submarine’s skin — ceramics, plastics, and other compo-nents– were found. Reportedly, after the BATON ROUGE had returned to her base in Norfolk two weeks later, divers conducting an underwater inspection found scrapes, dents and two minor gashes to her port ballast (one of two on the submarine). Fortunately, the accident did not cause any injuries or deaths.
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Why was the BATON ROUGE there?
The U.S. Navy has not released an explanation of why the BATON ROUGE was operating so close to the Russian coast. However, sources within the Pentagon reportedly have said that the BATON ROUGE was on an intelligence gathering mission at the time of the collision. This explanation has been offered in other press accounts of the collision as well.
There are several kinds of intelligence missions that could, at least in principle, have brought the LOS ANGELES class submarine so close to the Russian coast. One is simply aimed at gaining experience operating in shallow waters as close as possible to the Russian coast Although one press account stated that “there is little if any tactical reason these days for American submarines to operate so close to Russian shores,” the U.S. Navy may not yet have reached the same conclusion. The gathering of intelligence with submarines may also be able to provide information on aspects of Russian naval operations that could be useful in helping to predict the movements of the Northern Aeet. According to knowledgeable sources in the Russian Navy: “Intelligence gathering is a routine activity of American subs near our coast. Typically, there are one to two American or British submarines operating close to the coast off Murmansk, one to three off the Kamchatka peninsula and one off the coast of Vladivostok. During naval exercises this number can increase by a factor of two.”
Gathering intelligence either inside or just outside Soviet territorial waters has been a long-term program of the U.S. Navy, and has been given names such as Holystone, Pinnacle, Bollard, and Barnacle. 2 These activities apparently include close-up photography of the undersides of Soviet ships and submarines; plugging into Soviet underwater communication cables to intercept high-level military and other communications considered too important to be sent by radio or other less secure means; observation of Soviet submarine-launched ballistic missile (SLBM) tests including monitoring of the various computer checks and other signals that precede test launchings; and the recording of voice signatures — the noises made by operating Soviet submarines. One possibility, consistent with reports that her mission was intelJigence gathering, is that the BATON ROUGE was on the mission to install (or recover) intelligence gathering devices from the seabed near the shore.
Press speculation that the “American submarine, which… was sitting at ‘periscope depth’, may have been using secret inter-ception equipment to monitor communications at nearby military bases” is implausible for two reasons; First, continuous radio interception of military communications can be accom-plished without the use of a submarine. Communications intercepts can be accomplished with surface ships operating from international waters, and intermittent interceptions can be accomplished with satellites orbiting in space. Second, a submarine periscope or antenna sticking out ofthe water can be observed by a variety of relatively long-range sensor systems – in particular by modem radars. As a result, unless there is a compelling reason to argue otherwise, it is unlikely that a submarine commander would be willing to keep a periscope mast deployed for a substantial period of time in such close proximity to a potential enemy’s surveillance systems and forces.
Could the BATON ROUGE have been trailling the SIERRA?
According to one Soviet press report, the collision was the result of a cat-and-mouse game between the two submarines. This possibility deserves detailed study, since it could indicate that the U .S. may still possess substantial capabilities to trail Russian ballistic missile submarines.3
Since the BATON ROUGE was operating covertly close to major Russian Naval facilities, it is highly unlikely that she would have used her active sonar as it would greatly increase the likelihood that her presence would be detected. It is also unlikely that she would have been using her long towed array. The length of such an array with towing cable is more than 1 km., many times the water depth at the place of collision. In addition, it is difficult to control an array’s orientation in the water without severely constraining the motion of a submarine. Such constraints are highly undesirable when operating in close proximity to potentially hostile forces. Thus, although using her towed array would substantially improve her detection capabili-ties; it is unlikely that the BATON ROUGE would have this type of sensor system deployed in shallow waters. Hence, she was almost certainly using only her fiXed passive sonar systems.
This conclusion allows us to estimate her detection and counter-detection capabilities against the SIERRA submarine that she was allegedly tracking.
There are three reasons why the submarine passive acoustic detection ranges would have been short in the place of collision. FIISt, in shallow waters, the ambient noise levels from wind-generated breaking waves are typically 10-100 times higher than those in deep water. This noise generates background signals that can mask the presence of a signal from even a nearby submarine. This mechanism results in markedly higher wind-generated sound power densities relative to those in deep water. In technical terms, the coherence of sound in shallow water is considerably lower than in deep water. This means that it is not possible to achieve shallow water array gains as great as those in deep water. Second, in shallow water, the acoustic signals from a target submarine will arrive at the acoustic detectors of a hunting submarine from many different directions and at different intervals. This is because sound waves generated by a submarine will be reflected from the constantly shifting ocean surface and from numerous locations on the ocean bottom many times before they arrive at the face of an acoustic detector. Since the signals from a target and from breaking waves both unpredictably come from many directions, there is no way to enhance the signal from a target submarine relative to that from interfering wind-noise by increasing the number of receivers and the size of array. Third, there are no sound focussing effects in shallow waters, as there are in deep water, that can make it easier to detect the submarine against the background of ocean noise. Such deep water effects can strongly focus the sound from a localized sound source like a submarine at well defined distant ranges in the ocean. At the same time these effects only weakly focus the diffusely generated sounds from wind-generat-ed noise.
Quantitative analysis shows that the shallow water detection range of the fiXed sonar of the BATON ROUGE against a SIERRA class submarine would only be a couple hundred meters – even if the acoustic conditions for detection were nearly ideal and the submarine was oriented so that its sensors could achieve maximum sensitivity. Near ideal acoustic condi-tions could occur only in extremely calm seas. For environ-mental conditions that are much more typical of the waters off Murrnansk, like those associated with a 10 knot surface wind, noise levels would be great enough to result in the same short detection range even if the BATON ROUGE were using a long towed array. Making matters worse, it is likely that the SIERRA may have encountered the American submarine from behind. In this circumstance, the BATON ROUGE would have had no ability to detect the approaching SIERRA, as the ftxed sonar on the submarine cannot detect the signals within a cone 60 degrees to the re~r of the submarine.
Even if some une~cted combination of events led to the detection of the SIERRA, the ftxed sonars on the BATON ROUGE could provide very little useful information about the direction and range of the SIERRA. These detection and tracking limitations are a consequence of the relatively small size of fixed hull arrays and the highly unpredictable and variable transmission efficiency of underwater sound.
The arguments above do not support the speculation that the BATON ROUGE was trailing the Russian submarine. It would have been very hard for the BATON ROUGE to do so in this particular situation.
Could the SIERRA Have Known That the BATON ROUGE Was There?
Clearly, the conditions for the SIERRA to detect the BATON ROUGE by passive acoustic means were no better. As we have learned from informed Russian sources, there are specific rules for the safety of submarine operations in such a complex environment. The area of a submarine’s operations is closed to any shipping. The submarine is supposed to “look” around by using her sonar every hour and every time when her depth of operation is changed. In order to do this a submarine has to move along a loop shaped trajectory, because her sonar is deaf in the aft direction.
It is possible also that Russian submarines may use their sonars in an active mode as a standard operational procedure, when they do not need to be covert in their home waters. The use of an active sonar could allow the SIERRA to increase her detection range to a couple of kilometers and to obtain much more detailed target location information. It appears, however, that she was not using her active sonar, since the American submarine would have heard the approach of the SIERRA and determined the bearing of the Russian submarine at a distance of at least several kilometers, which is enough to take care to avoid a collision. In fact, in this situation, the BATON ROUGE would have detected the Russian submarine long before she was detected by the SIERRA.
It is also interesting to consider two related questions: What were the potential capabUities of the Russian anti-submarine warfare (ASW) forces to detect the BATON ROUGE? Would it have been possible to avoid the accident if the Northern Aeet ASW forces acted properly?
Most likely, the American sub had to pass a Russian seabed passive (or active) sonar system near the approaches to the Russian shore. The detection range against a quiet LOS ANGELES class submarine of such a passive system might be about 1-5 kilometers in the best conditions of a calm sea.
According to the Russian Chief Navigator Valery Alexin, several fiShing ships were present, the screws of which generated noise similar to that of the American submarine. These fiShing ships might substantially mask the BATON ROUGE, although it seems improbable that such ships were actually present, since the Russian Navy is typically very cautious about permitting civil ships in the operating areas. Using a passive seabed system the location of the submarine could be determined more accurately than by using a towed array, but probably not better than 1-2 km. If stationary active sonar techniques were employed, the detection range would be restricted by surface and bottom reverberations and might not exceed 5 km.
The BATON ROUGE could also have been tracked either by a ship’s active sonar at a range of no more than 1 or 2 km, or by sonobuoys which could be deployed by aircraft. The detection range of active sonobuoys most probably was not more than 1 km for this particular case. A possible means of locating a submarine more precisely could be airborne magnetic anomaly detection (MAD} and lidar (lasers) sensors.
As a result, il appears unlikely that the Russian ASW Forces detected the American submarine before the collision. As the estimates above indicate, substantial capabilities would be required to keep even a relatively small area safe from invasions by foreign submarines. Most probably, on routine duties, less capable forces are deployed, and this might be the reason why the American submarine was not detected.
Despite the claims of some press reports, it appears likely that neither submarine heard the other before the collision and that the collision was an accidenl Playing an extended cat-and-mouse game would have been impossible in that area because both subs possessed only very short-range detection capabilities. Moreover, there are no reliable means available to submarines that would allow them to operate both covertly and safely in such a complex environment as the shallow waters of the Barents Sea.
The circumstances of this collision suggest that, at least in some environmental conditions, if carefully operated, modem Russian submarines are almost impossible to detect by passive acoustic methods, even by the highly capable ASW forces of the United States. If true, this has important implications for the options available to Russian policy-makers as they decide how to implement the nuclear reductions called for by the START Treaty and the follow-on Bush-Yeltsin agreement as well as possible future deep reductions in strategic nuclear forces.
The great emphasis that has recently been placed on assuring the safety of the nuclear weapons of the former Soviet Union stands in sharp contrast to the circumstances of this incidenl The collision illustrates that covert operations of foreign submarines close to Russian Naval bases can create dangerous situations that may result in undesirable outcomes. More than half of the 54 Russian strategic submarines, each with 16-20 submarine launched ballistic missiles, are still based near Murmansk. The benefits accrued by U.S. attack submarines operating so close to Russian port facilities may be offset by the risk that a nuclear weapons related accident might eventually result.