Articles 3 and 4 define and arm small carriers

Article 3 replaces the Washington treaty's carrier definition with a role-based test: a surface warship must be designed exclusively to carry, launch, and recover aircraft. Merely adding a flying-off or landing platform to a battleship, cruiser, or destroyer does not move that ship into carrier tonnage. The clause also bars fitting existing capital ships with landing platforms after 1 April 1930. Article 4 then stops carriers at or below 10,000 standard tons, or 10,160 metric tons, from mounting guns above 6.1 inches or 155 millimetres. Together the provisions show negotiators closing both classification and armament routes by which a small flight-deck ship might retain cruiser-like fighting power.