Put your SOKS on! SOKS stands for System Obnarujenia Kilvaternovo Sleda. It is a non-acoustic wake/submarine detection system.The SOKS sniffs the water in search of radioactive particles the size of atoms as well as checking it for changes in its refractive index and chemical composition. SOKS is not one sensor but rather a suite of various sensors working together.
A nuclear submarine cooling system will often leave a faint trail of radioactivity in its wake. Similarly, it will release traces of various metals (zinc, nickel and so on) coming from its pipes. Furthermore, the water released by the reactor’s cooling system will be warmer than the ambient water temperature… Finally, a submarine, when traveling through water, will “stir” that body of water, creating millions of miniature air bubbles, therefore changing the density of the water. All those traces can remain behind a submarine for hours, creating a trail of some sort. The SOKS basically is made up of several instruments measuring those parameters.
In theory, this will help a Soviet/Russian submarine follow the trail left by other (NATO) nuclear submarines. The Soviets operationally used SOKs for the first time in the late 1960’s. Ironically, it seems the Soviets researched and developed SOKS because their passive sonars at the time were of mediocre quality. Nowadays, with modern electronics and modern technology, the Russians have been able to improve on both sonar and SOKS technologies.
Does it work and is it accurate ? Well, info is lacking on this subject… The Russians, usually more than happy to share data on their latest weapon platforms do not share much about this system in particular. A lot of it is classified but it seems that their brand new Yasen class submarines have been equipped with the SOKS system, too…
The Russians, however, are not the only ones using such a system, it seems: On the 8th of May 2019, a British sub was spotted with a Wake Detection System, too: British sub HMS Talent arrived in Gibraltar sporting a brand new Wake Detection System of its own.