The ships were purchased on 10 February 1941 by the Navy Ministry for the price of ¥48,346,000 and their armament and aircraft cost an additional ¥27,800,000. The cost to convert the two ships was budgeted at ¥38,073,000, for a grand total of ¥114,219,000. "Kashiwara Maru" and "Izumo Maru" were temporarily referred to as No. 1001 Ship ("Dai 1001 bankan") and No. 1002 Ship respectively to keep their conversions secret. "Jun'yō" was initially classified as an auxiliary aircraft carrier ("Tokusetsu kokubokan"), but following the loss of four Japanese fleet carriers in the Battle of Midway, she was redesignated as a regular carrier ("Kokubokan") in July; "Hiyō", completed after the loss of the carriers, received that designation from the beginning.