Although naval doctrine changed, design practices remained until the later parts of World War II when the German Kriegsmarine suffered ever-growing losses of submarines in the Battle of the Atlantic.
This led to the eventual reintroduction of the teardrop hull in submarines, being employed in various forms on virtually all large undersea military vessels today.
Because the term refers not to any exact shape, but rather to the abstract concept of a hull shape optimized for underwater travel, and more specifically the physical manifestation of this idea in actual submarines as limited by material sciences and the design requirements placed upon the vessel, whether or not any specific vessel exhibits a teardrop hull depends on the subjective interpretation of the term itself.
There also exists an option for a hydrodynamically optimized single hull nuclear submarine such as the Skipjack-class, but creating large 3D-curved plates out of thick, high-strength metal remains prohibitively expensive.
As size increases, the greater beam of the boat allows for the use of angled torpedo tubes firing through the sides of the hull while leaving room in the bow for a much larger sonar array.
American designers settled on a modified version of the Delphin's cruciform arrangement (a Greek cross viewed from behind); they rejected the alternative of an x-arrangement for its complexity, but it was accepted and used by the Dutch, Swedish, Australian and German navies among others, for its ability to snuggle closer to a shallow seabed without striking the rudder on the sea floor.