Military Intelligence Directorate



Intel Report



Jan 2, 2010


The following is an analysis of NATO's undewater hydrophone arrays, known as SOSUS, which occupy a vast area of the ocean floor throughout the North Atlantic and Norwegian Sea. To see the general location of these arrays, please review the SOSUS Map (which is also located in the Chart Room at Northern Theater Headquarters). This report will provide you with our best estimate of the system's capabilties for planning purposes. Included are formulas for determining the sensitivy of NATO's hydrophones and the likelihood of detecting one of our submarines.

What this report does not contain, however, ar the actual locations of the SOSUS hydrphone tanks which would allow our submarines to evade detection more easily, nor does it contain information on the actual hydrophones themselves, or the route of the signal or the method of processing for identification/classification purposes. Such information would be the pronvince of the FSB, and could only be extracted at great risk and expense. Still, this could be procured with the proper authorization. (See your Intel/CI Officer about making this a high priority when submitting intelligence requests.)

Current status of SOSUS

The SOSUS arrays are made up of a vast number of hydrophone clusters which were laid along the Atlantic floor as early as 1947, with some of the existing system still using hydrophones placed during the 1960's. While the SOSUS system is quite dense, we believe that the hydrophone technology and wiring are quite dated, and when combined with the more refined tactics for evasion among our submarine commanders (e.g., slipping between bands of water of different temperatures) we believe the actual range of pickup is actually rather poor by modern standards, and often highly unreliable.

Detection Capability

Based on our best estimates, we have developed the following formula to determine the risk of being detected by the SOSUS system. We emphasize that this is only an estimate; we have no idea if these figures are correct without gaining access to special records in Norfolk, Va. (Please contact your Intel/CI Officer to see if he can arrange such a mission through the FSB.) Without such verification, we believe the accuracy of this report could be off the mark by as much as 50%. You may want to make allowances for such errors in your planning.

To determine the base chance of detection, use the following figures:

Class --

EQuiet: 10% chance of detection per 8 hour period.
VQuiet: 20% chance of detection per 8 hour period.
Quiet: 30% chance of detection per 8 hour period.
Noisy: 40% chance of detection per 8 hour period.

Next, consider the effect of the sub's speed, and the sea state.

Speed --

Creep speed = No change
Cruise speed = 50% increase in chance of detection
High speed-flank speed = Double chance of detection.

Thermocline -- There is a further 50% reduction in chance of detection if the sub is at shallow depth, above the thermocline. (If the sea state is 5 or above, or if the depth is shallow, there is no thermocline.)

Environmental factors -- Then factor in the various environmental conditions, transients or change of maneuver. (See Environment and Special Modifiers in Harpoon 4, page 4-11.)

The final result is the actual chance of detection for a given sub.

Skill of the sub commander

A veteran sub captain can also make a difference in the ability to evade detection, as he will likely be more familiar with the underwater currents as well as tactics learned from the Cold War. It is assumed that the newer the boat, the more senior the commander. Thus, veteran captains are considered to be commanding the following boats:

-- All "improved" classes (Imp. Akula, Imp. Victor III, Project 636 Kilo)

-- All SSNs numbered over 400.

These commanders will have a 40% chance of completely evading detection during any 8-hour period. (If sub is detected, roll D100 @ 40% to see if it "escapes" detection.)


Due to the dedicated nature of the hydrophones and the powerful processing used by NATO's land-based computers, we assume that a great many SOSUS detections are automatically identified by class.

Range, bearing and reliability

Since hydrophones are omni-directional there is no way to determine the sub's location in relation to the array. The speed of the sub is also unknown. There is also some amount of relay and processing time as well as the time needed to notifiy the appropriate command, during which time the accuracy of the reported location starts to decay even further. We believe it is possible that by the time a ship captain or air base commander is alerted to the sub, that the reported position may only be accurate to within 15-20 miles .

This concludes the brief on SOSUS detection. We hope the above information will be of value in the weeks ahead.


The CAESAR System

The CAESAR System is a small field of hydrophone arrays located in the western Barents Sea between Norway's North Cape and Svalbard as shown on the SOSUS Map. It is our own version of SOSUS, which dates back to the 1950's and 60's. Because of its early technology and the lack of maintenance it has received over the years, we estimate this system is only half as effective as SOSUS. Thus, the chance of detecting a NATO sub by CAESAR can be determined by halving the detection probability of SOSUS.