A historical gun's designation can distinguish weapons that share the same nominal bore, as with the American five-inch/25, five-inch/38, and five-inch/54. Converting all of them to 127 mm removes information carried by those names. National conventions also complicate comparison, including whether a bore is measured across the lands or grooves of its rifling. The French 138.6 mm gun illustrates how the original designation may resist a convenient rounded conversion. World of Warships is defended on different grounds: a consistent metric display makes its calibre-based penetration calculations easier for players, even where the display departs from historical terminology.
Notable Point · 2:30:10-2:32:36
Why historical gun names cannot always be reduced to millimetres
Original weapon designations preserve distinctions that a metric conversion can hide, while a game's uniform units serve its own calculation rules.