The proposed 15-inch 50-calibre gun belonged to the period immediately after the First World War, while the mid-to-late 1930s design used a 45-calibre barrel. That later gun is described as lighter than the existing 15-inch 42-calibre weapon, allowing faster turret movement while improving range. The preference for moderate barrel lengths also reflects barrel wear: a 50-calibre weapon offers more range but requires more frequent replacement. Ships operating in the Pacific depended on an industrial and supply base in Britain. A small reduction in maintenance demand could make a gun more useful by keeping it available when needed.
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British naval gun length, barrel wear, and distant bases
The later 15-inch 45-calibre proposal combined lower gun weight with better range, while moderate barrel lengths reduced replacement demands far from British bases.