The consequences of common German-Italian naval armament

What if Germany and Italy standardized on a 135 mm dual-purpose gun and triple 15-inch capital-ship turrets?

The dual-purpose gun could improve fleet standardization, but twelve-gun Bismarck and Littorio designs would trigger stronger Allied battleships and expose difficult integration problems.

Common weapons would require Germany and Italy to reconcile different shells, mountings, fire-control practices, and manufacturing standards. A successful 135 mm dual-purpose system could encourage larger destroyers and simplify secondary batteries on capital ships. Fitting triple 15-inch turrets would raise Bismarck and Littorio to twelve-gun broadsides, although projectile and propellant quality would still matter as much as nominal caliber. Britain would answer such ships with stronger Lion-class designs or other escalations, so Axis standardization would reshape the wider arms race rather than grant an uncontested advantage.