An 18-inch naval gun adds considerable weight and complexity over a 16-inch weapon. The larger shell does not offer enough general improvement to justify those penalties in most designs. Armor penetration is the main circumstance in which the larger caliber becomes worthwhile. The tradeoff shows why maximum gun size must be judged against the cost imposed on the whole ship.
Notable Point · 0:00-0:22
The narrow case for 18-inch naval guns
An 18-inch gun offers limited general gain over a 16-inch weapon once weight and complexity are counted; armor penetration is the main exception.