Submarines of the Soviet Navy were developed by numbered "projects", which were sometimes but not always given names.
During the Cold War, NATO nations referred to these classes by NATO reporting names, based on intelligence data, which did not always correspond with the projects.
See: The NATO reporting names were based on the British (and later American) habit of naming submarines with a letter of the alphabet indicating the class, followed by a serial number of that class.
Most Russian (and Soviet) submarines had no "personal" name, but were only known by a number, prefixed by letters identifying the boat's type at a higher level than her class.
Those letters included: Any of those prefixes could have С (S) added to the end, standing for специальная (spetsialnaya) and meaning "designed for special missions":