Both ships were significantly modified throughout their careers. During and shortly after World War I, the horizontal armor of the ships was improved, including the roofs of the conning tower and the gun turrets. Their deck armor was increased to , and eight /50 caliber anti-aircraft guns were installed. Following the signing of the Washington Naval Treaty in February 1922, modernization work was strictly controlled. The treaty governed what modifications could be made to existing ships, and included restrictions on what could be changed or added. Displacement could rise by no more than and no alterations of any kind could be made to the main battery guns or mounts. The primary areas that could be improved were those that concerned defense against aerial and underwater attack, along with propulsion systems.