Russian Navy deployed Marine Mammals to Defend Base in Syria
Flag The Russian Navy deployed marine mammals to Tartus in Syria during September-December 2018. The animals, most likely seals, were positioned next to the harbor defense units which were also being boosted around that time.

It seems most likely that they were there to perform harbor defense duties of some kind. The Russian Navy is known to train seals to perform anti-diver operations. They could possibly also be used to protect the undersea pipe lines near the port which have been targeted by opposition divers.

Russian Navy In Tartus Syria - Covert shores
Based on analysis of Google Earth Imagery, the marine mammal pens were present on September 30 2018, and again on November 8 2018. But they were not present on February 4 2019. Using lower resolution Sentinel Hub data, with correspondingly lower levels of confidence, they do not appear to have been present on September 18 2018. But were there by September 28. And they appear to have been removed by December 22 2018.

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The marine mammals likely came from the Russian Navy's Black Sea Fleet. There is a unit based near Sevastopol in Crimea. The Black Sea Fleet regularly deploys warships to Tartus. And, controversially considering the Montreux Convention, submarines also.
Russian Navy In Tartus Syria - Covert shores
source Capt_Navy, Twitter

This unit, at Kazachya Bukhta near Sevastopol, was the Russian Navy's main marine mammal establishment during the Cold War. However it found itself in the newly independent Ukraine after the fall of the USSR, and was inducted into the Ukrainian Navy. Like many units it lapsed into non-operational status and was used as a tourist attraction. More recently it was re-established as an operational unit, but then captured by Russia during the annexation of Crimea in 2014. The unit is still active and is known to use dolphins. It may use seals also.
Russian Navy In Tartus Syria - Covert shores

It is unclear why they were there for only a few months. Their mission may have been specific and of a fixed duration. Or possibly it was an experimental deployment to build the Russian Navy's resurgent marine mammal program's capabilities. Or possibly the deployment was not considered a success and was abandoned.

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The port is defended by an array of anti-sabotage units. There are counter-divers armed with APS-5 underwater assault rifles and SPP-1 underwater pistols. There are two Pr.21980 Grachonok Class anti-sabotage boats, four assault boats and an array of smaller craft used to patrol the harbor. Russian warships are generally equipped with pedestal mounted multi-barrel anti-diver grenade launchers.
Russian Navy In Tartus Syria - Covert shores

In June 2019 five underwater pipelines have been damaged and put out of order after a sabotage attack. Divers placed explosives on the pipeline off the coastal town of Banias, about 25 miles north of the port.

The Syrian Navy has some missile boats (OSA and Tir), and reportedly some Raptor assault boats (although these may be Russian Crewed?). But has a limited ability to defend the port against divers or deal with underwater explosives.
Russian Navy In Tartus Syria - Covert shores
Russian supplied PETYA Class light frigate of the Syrian Navy. The sole remaining vessel is believed to be inoperable and likely decommissioned. Since this image was taken the main armament has been removed.

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Russian Navy In Tartus Syria - Covert shores

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