Russian Kilo subs and seabed sensors involved in 2 NATO submarines' detection

This depth-map indicates the choke-points (narrows) where both NATO submarines entered the Mediterranean Sea, ie. the US Virginia class through the Strait of Gibralter (on the map, extreme left) and the Dutch Walrus class (lower, right corner) near Port Said, Egypt.
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WALRUS (SSK) AND VIRGINIA (SSN) DETECTION DETAILS

Various Russian sensors were involved in the recent detection of two NATO submarines. Sensors included:

-  publically admitted, over-water (ASW helicopters) and surface ASW ships (see BACKGROUND)

-  (more secretly) Russian Kilo submarines, near stopped, operating at choke-points. 

-  equally secret were seafloor sensor arrays used: near the Strait of Gibraltar; another north of Port

   Said at the northern opening of the Suez Canal; and yet another outside of Russia's Tartus (Syria)

   naval base.

Russia's Main (Military) Intelligence Directorate (known as GRU) reported that a Dutch Walrus class submarine transiting the Suez Canal emerged into the Mediterranean Sea only to "rendezvous" with, be intercepted by, various ASW sensors.

GRU was already aware that the Dutch sub, after Indian Ocean regional ops, had then transited the  Suez Canal from south to north with a known time of emerging into the Med. This made it quite easy for a Kilo (from the Black Sea fleet) to cue or "rendezvous" with the Dutch sub. This Kilo gained valuable intelligence on characteristics of some upgrade work done on the Dutch sub.

The US Virginia class SSN had earlier been (predictably) tailing the Admiral Kuznetsov carrier group from a range of 70km. As the Virginia class sub transited the Strait of Gibraltar (traveling from west to east into the Med) it was detected by a fixed seabed sensor array (perhaps in cooperation with local assistance). The detection was later confirmed by Russian helicopter dipping sonars (active) and ship bow sonars.

GRU further reported that, by their behaviour, the Walrus and Virginia class subs positively detected the presence of the Kilo subs.

BACKGROUND

Allen Cone, for UPI reported on 9 November 2016 "Russia: Dutch sub tried to approach, spy on aircraft carrier" http://www.upi.com/Top_News/World-News/2016/11/09/Russia-Dutch-sub-tried-to-approach-spy-on-aircraft-carrier/6431478701381/

"(MOSCOW, Nov. 9 (UPI)) -- A Dutch submarine attempted to spy on a Russian aircraft carrier after approaching it in the eastern Mediterranean Sea, a Russian Defense Ministry spokesman said Wednesday.

The Northern Fleet's anti-submarine ships forced the sub to leave the area near Russia's Admiral Kuznetsov aircraft carrier, spokesman Maj. Gen. Igor Konashenkov said in a statement.

"The clumsy attempts to carry out dangerous manoeuvres in the direct proximity of the Russian group of warships could have led to grave navigation consequences," he said.

He said two anti-submarine ships, Severomorsk and the Vice-Admiral Kulakov, at 6:50 a.m. spotted a Dutch navy sub, which neared the Northern Fleet's aircraft carrier group for surveillance purposes."

He said the crews "easily identified the submarine that was 20 kilometers [12.5 miles] away using the standard onboard hydroacoustics systems and data obtained from anti-submarine helicopters Ka-27 PL. Despite the submarine's attempts to evade surveillance, a stable hydroacoustic contact was established with it."

Konashenkov said they monitored the submarine for more than an hour and forced it to leave the carrier group.

"It is noteworthy that submarines of such class, having big displacement, are not fit for reconnaissance," the spokesman said.

The ministry official also said the Russian navy's aircraft carrier group regularly spotted NATO's submarines on its way to the Mediterranean.

Earlier this month, he said the USS Virginia was trying to spy on Russian vessels.

Last month, Russia's Northern Fleet's the Kuznetsov aircraft carrier, accompanied by the Pyotr Veliky battle cruiser, the Severomorsk and Kulakov, and support vessel were sent to the Mediterranean to hold drills and strengthen capabilities."

Please connect with Submarine Matters articles:

-  Russia set to unleash carrier aircraft and SLCMs on IS in Syria of  31 October 2016, and 

-  Russian carrier Admiral Kuznetsov may conduct first airstrikes (against IS), October 17, 2016.

Pete