 No retained capital ships or aircraft carriers shall be reconstructed except for the purpose of providing means of defense against air and submarine attack , and subject to the following rules : The Contracting Powers may , for that purpose , equip existing tonnage with bulge or blister or anti @-@ air attack deck protection , providing the increase of displacement thus effected does not exceed 3 @,@ 000 tons ( 3 @,@ 048 metric tons ) displacement for each ship . 
