Why the Royal Navy chose the 4.5-inch gun

Why did the Royal Navy adopt the 4.5-inch gun?

It was a compromise between four-inch high-angle and 4.7-inch naval guns, developed as a useful dual-purpose caliber.

The caliber was a practical British development choice rather than a uniquely optimal solution. Designers wanted a weapon between the existing four-inch high-angle gun and the standard 4.7-inch naval gun. The result combined useful shell weight with a caliber suited to high-angle work. The United States followed a different path by developing its five-inch gun across several roles.