Why a twelve-gun treaty cruiser breaks the design box

What problems arise from a treaty cruiser armed with twelve 12-inch guns?

The battery cannot fit a balanced 10,000-ton hull; the design must be overweight or severely compromised.

Four triple 12-inch turrets cannot fit a balanced cruiser within 10,000 tons. Such a design would have to exceed the limit, sacrifice substantial speed, or belong to a different treaty system. If Britain nevertheless had forty of these ships before 1930, it would possess a major advantage. The assumed fleet therefore requires a change in the design constraints as well as a decision to build more ships.