The treaty replaces the Washington definition with one centered on a warship's exclusive purpose and its ability to launch and land aircraft. Merely fitting a flying-off platform to another ship type did not make it a carrier. A further prohibition on landing decks for existing capital ships reflects anxiety that navies might combine battleship and carrier capabilities in one hull. These definitions prevented a navy from escaping carrier rules simply by presenting aviation equipment as an accessory to another combatant.
Chapter · 25:40-26:33
The 1930 treaty defines the aircraft carrier
Article 3 classifies purpose-built flight-deck ships as carriers while preventing existing capital ships from becoming hybrid battlecarriers.