http://www.armscontrol.ru/subs/snf/snf03222.htm
another nice example when detection can be very hard
and most importantly, the conclusions we have been looking forQuantitative analysis shows that the shallow water detection range of the fixed sonar of the Baton Rouge against a quiet23 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 conditions could occur only in extremely calm seas. For environmental conditions that are much more typical of the waters off Murmansk, like those associated with a 10 knot surface wind,24 noise levels would be high enough to result in the same short detection range of 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 fixed sonar on the submarine cannot detect the signals within a cone 60 degrees to the rear of the submarine.
So, the Maximum range an Akula klass submarine can be tracked pasively is 10km , thats more than a magnitute ten times smaller than represented in the game . This proves there is something seriously wrong with the sub detection ranges in the gameIt is not difficult to estimate that with detection ranges at several tens of kilometers, the width of the "corridor" may be no less than 5-10 km; and with detection distances of less than 5 km, it decreases to 1-2 km. In this connection we stress the importance of the circumstances which will not depend on the enemy. Firstly, during the tracking process, both the conditions for sound propagation and the level of external noise will change. Shallow water regions are characterized by fluctuations in propagation losses which reach up to 5 dB. In particular, an average detection range of 5 km will result in the upper limit "corridor" fluctuating from 2-3 to 8-9 km (model A). The tracking submarine will hardly be able to respond adequately to such changes during long periods of weeks and months. Secondly, the strategic submarine may also change the mode of its movement. We propose that it will change to another depth. As a result the algorithm for the signal filtration will stop being optimal and the tracking submarine may lose its target. Frequently submarine collisions result from one of them changing their operating mode. At small distances, in which tracking takes place, the integration time (the time needed for accumulating information on the signal in order to decide that a target is detected) is very important. Our calculations assumed an integration time of 100 seconds. Even if the tracked submarine moves at a minimum speed of 5 knots (2.5 m/s), during the time it takes to accumulate the signal, it has moved 250 m before changes in the target's behavior are detected. Obviously, with such a method for signal processing, attempting to tail at short distances is simply dangerous. Decreasing the accumulation time to 10 s results in the "dead distance" being decreased to 25 m, but by doing this the detection threshold is raised by 5 dB (see formula A2.4) and this leads to a reduction in the maximum achieved detection range. If in our computation the detection distance is 10 km, then with a 10 second accumulation, it is lowered to 6 km (model A). If it reached 5 km, then an increase in the detection threshold by 5 dB is equivalent to a decrease in the maximum distance to 2-3 km. One of the biggest problems that occurs during tracking is localizing the target with the necessary accuracy. At short distances (less than 5 km), the precision for determining the distance to the target must be no worse than 0.2-0.5 km. To provide such accuracy the enemy will have to have good knowledge of the conditions for signal propagation in a specific region of military activity within a given period.(32) Horizontal inhomogenities in the environment will lead to fluctuations in the conditions for signal propagation so that the lower limit of the "corridor" will also fluctuate because of changes in the accuracy of localizing the target. The reasons cited permit the claim that an estimate of the detection distance at 10 km is the limit at which it is technically possible to realize continuous tracking, while ensuring covertness and guaranteeing the potential of avoiding collisions. If this is true then it is possible to see (see Figure A2.2a, A2.4a), that even in the most favorable conditions for sound propagation the "Los Angeles" class submarine can not execute this task.