When submarines were no longer required to operate and transit on the surface, the requirement for hull forms optimised for surface travel could be replaced by designs optimised for undersea travel.
As far back as the 1917
R Class of the Royal Navy it was recognized that high underwater speed required different shapes than surface seaworthyness. The
R's were the first submarine hunter-killers and even if the technology was not mature enough to make them successful in that role they had some features, the bulbous bow shape in particular, that greatly improved their submerged performance relative to those boats with ship-like stems, either straight or flared.
USS Albacore (
AGSS 569) is generally considered the forerunner of the teardrop shape submarine whereas the Soviet Navy retained a basic
Type XXI hull form as late as the
Project 641B (NATO
Tango Class) introduced in the late 70's. The OP's linked photo looks to be a
Project 641 (NATO
Foxtrot Class) which preceded the Tango's into service. Cold War accounts of
Foxtrot and
Tango operations indicate that these boats spent more time surfaced than submerged so retaining a flared stem for improved seaworthyness made sense.
The first true teardrop hull in Soviet service was probably the
Project 671 (NATO
Victor Class) first reported from 1969 although Soviet designs had featured much smaller and very streamlined sails as far back as the
Project 627 (NATO
November Class) and
Project 569 (NATO
Echo Class) from the late 1950's and early 1960's.
For the
R Class see:
http://www.battleships-cruisers.co.uk/r_class.htm
For
USS Albacore see:
http://www.ussalbacore.org/