Why Kawachi and Settsu mixed 12-inch gun lengths

Which Japanese dreadnoughts carried two different lengths of 12-inch gun?

Kawachi and Settsu carried four 50-calibre and eight 45-calibre 12-inch guns.

The Kawachi class, comprising Kawachi and Settsu, combined two lengths of 12-inch gun. Each ship carried four 50-calibre weapons and eight 45-calibre weapons. Although every gun fired a nominally 12-inch shell, the different barrel lengths made the battery less uniform than the calibre label suggests. The arrangement helps explain why a true dreadnought was expected to standardise its main armament.