When did they decide to abandon ship's bows?

[msxyz]

The "bow" in post war subs is actually a dome containing an array of transducers. The principle is more or less the same of a sinthetic aperture antenna but this is designed to pick up sound, not radio waves.

That looks like a soviet Romeo submarine or a similar class. It has a slight, protruding bow that helps breaking the waves but it's not the main function of that bow, as it holds a U-shaped sonar array.

Basically, when submarines began spending more time underwater than surfaced, the classic bow shape (that helps seakeeping) was dropped in favour of designs that guaranted lower resistance underwater.