The armour problem created by eighteen-inch guns

Once a design carries nine 18-inch guns, the question of what its armour can realistically defeat becomes acute. Protecting against shells of that size would be extremely difficult, so K3 could not be treated as an invulnerable capital ship. Its answer included a 305-millimetre internal belt inclined at 25 degrees. The angle makes an incoming shell pass through a greater effective thickness than the nominal figure alone suggests. Escalating gun power forced designers toward increasingly demanding armour geometry as well as heavier plates.