K3 as the fast nine-gun eighteen-inch extreme

K3 is presented as the scariest of the British alternatives and as a battlecruiser of sorts. Its defining feature is a battery of nine 18-inch guns carried by a ship with high speed. That combination would let it threaten heavily protected opponents without accepting every battle offered to it. Its possible survival into the Second World War is a counterfactual, not evidence about a completed ship. The exercise establishes the extreme performance problem before turning to armour and secondary weapons separately.