Why a giant Italian battlecruiser changes the treaty system

How would the Italian fleet and naval balance change if the proposed large battlecruiser were built instead of the Littorio class?

Its 18-inch armament would transform treaty negotiations and foreign building programs, creating an arms race that Italy was poorly placed to sustain.

The proposed ship carries eight 18-inch guns in four twin turrets and originates in a 1921 design context. Building it instead of the Littorio class would not be a simple one-for-one substitution because such a program would alter the assumptions behind the Washington Naval Treaty and provoke different foreign capital-ship responses. A target speed between thirty-five and forty knots would further push size, machinery, and cost beyond the range of an ordinary treaty battleship. Stacking boiler rooms to shorten the hull is treated as a particularly risky choice because damage or failure in the lower space could also disable the machinery above it. The panel argues that the resulting arms race and industrial burden would probably leave Italy worse off.