I believe Russia likely has subs that are thin often referred to as "Silver dollar" shaped; that can sit on the bottom of the ocean like a Stingray buried in the sand! They likely have air recirculation systems and perhaps extra long telescoping periscopes that can pump in fresh air.
They could indeed stay submerged on the bottom of the ocean for years on end if food were "dropped" to them.
Thomas Paul Murphy copyright 2014
Originally published on 10 21 2014 at: www.themilwaukeeandwisconsinnews.blogspot.com