The carrier gun limit was an anti-evasion measure with consequences beyond aviation. A navy might otherwise classify a cruiser-sized warship as an aircraft carrier by adding only a token flight deck. The result could have been a heavily armed fast ship that consumed carrier rather than cruiser allowance. A deliberately exaggerated sketch combines 10,000 tons, 32.5 knots, 24 aircraft, nine six-inch guns, and eight five-inch guns. It shows why weapon limits were needed to protect the treaty's allocation system.
Notable Point · 2:43-4:14
Why carriers were limited to six-inch guns
The six-inch limit on carrier guns closed off a loophole in which a nominal flight deck could conceal an eight-inch-gun cruiser.