Why the 76 mm naval gun became a durable sweet spot

Why has the 76 mm, 3-inch, or 12-pounder caliber remained so popular as a naval gun?

It is large enough for useful shells, fuzes, range, and damage, yet compact and light enough for rapid fire and flexible mountings.

The 76 mm calibre balances shell capacity against the size and weight of its mounting. From the late nineteenth century, it was large enough for useful specialized shells while remaining suitable for a relatively light, quick-firing gun. Early postwar 3-inch shells could accommodate proximity fuzes that contemporary 40 mm shells could not. Later developments extended the calibre to guided ammunition. Useful range and destructive effect allowed the gun to serve several roles without demanding a large mounting. Long experience with its ballistics also made further development easier.