Trying to keep up with all of the similarities/differences (and names) of the numerous Soviet submarine classes in this game can be confusing for many.
Check out the extensive chart (pdf format) at the bottom of this link which might be helpful and informative. It includes notable accidents and loses (and there were a lot!) during the Cold War.
http://www.rjlee.org/blog/2012/03/03...ntal-timeline/