Submarines of project 641B — a series of Soviet diesel-electric submarines (Tango NATO classification). Is an upgrade of project 641. By construction, the boat is made double casing, has seven sections: the first (bow) torpedo; the second and fourth fore and aft of the battery; the third — the Central post; the fifth — diesel; sixth — electromotive; seventh — aggregate and residential. The first, third, and seventh compartments are adapted for the evacuation of the crew.