 The Treaty authorized conversion of two battleship or battlecruiser hulls into aircraft carriers of up to standard displacement.The incomplete battlecruisers "Amagi" and were initially selected, but the Great Kantō earthquake of 1923 damaged "Amagi"s hull beyond economically feasible repair, and "Kaga" was selected as her replacement.The formal decision to convert "Kaga" to an aircraft carrier was issued 13 December 1923, but no work took place until 1925 as new plans were drafted and earthquake damage to the Yokosuka Naval Arsenal was repaired.