My guess is that you either think the Project 877 and Project 636 are individual submarines or that you think they are the same because they both share the name Kilo. Neither is true. The Project 877 and Project 636 are distinct submarines classes with different specifications, with several individual submarines in each class. The Alrosa is a modified Project 877, just one sub out of 11 Russian Project 877s in DW.
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