Why did Soviet, Italian, and German battleships retain mixed secondary batteries while other navies adopted dual-purpose guns?
Short answerSeparate batteries appeared to maximise each role, whereas dual-purpose guns required a compromise those procurement cultures disliked.
NotesA six-inch surface battery offers more range and penetration than a five-inch gun, while a four-inch weapon can deliver a better anti-aircraft rate of fire. A five-inch dual-purpose system accepts compromises in both roles to simplify the ship's armament. Authoritarian procurement cultures could favour nominal perfection in separate roles over that operational and logistical compromise. Mixed batteries follow from the desire to maximise each individual task rather than the whole system.