Covert Shores reports the Rubin Design Bureau, which has designed most of Russia and the Soviet Union’s submarines, has proposed a submarine for the Russian Coast Guard.
“The BOSS (Border and Offshore Submersible Sentry) submarine is a concept which has been around for a few years. It is unlikely that Russia will ever build it, but it is all the same an interesting possibility.”
Apparently, the Russian Coast Guard did not ask for a submarine, but the design bureau thinks, even if they don’t want it, it might be exportable.
It’s small, about the size of a World War II vintage German Type VII U-boat, “…60 – 70 meters (197 – 230 feet) long depending on customer configuration, and displaces around 1,000 tons.” Being submersible it could submerge to wait out rough weather.
I do kind of like the way it’s equipped, boat for boarding, VTOL UAS for search, gun for firing warning shots, 10 km range small surface to surface missiles for engaging small fast highly maneuverable targets, and torpedoes capable of forcibly stopping any size vessel.
Chuck Hill's CG Blog 
It is interesting. In someways these are a modern manifestation of cruiser submarines from the early decades of the 20th century. I have wonder whether as things become more dangerous on the surface whether there is mileage in the submersible ship idea.
In this case it may be a question of, is it better for your sentry to be visible or invisible?
Russians are very concerned about attacks on their fleets while in harbor. It keeps happening to them.
Their maritime force protection isn’t as deep as their aerospace defences.
They are a land power though so those attack are a nuisance.
I expect they will be in Odessa by late summer.