In February 1938 the ship replaced her A4N biplanes with nine Mitsubishi A5M "Claude" monoplane fighters. The division supported Japanese operations in Southern China in March–April and again in October. Captain Kiichi Hasegawa assumed command on 15 November 1939. "Ryūjō" was given a refit that lasted from December 1939 through January 1940 and became a training ship until November when she became the flagship of Rear Admiral Kakuji Kakuta's Third Carrier Division. Hasegawa was relieved by Captain Ushie Sugimoto on 21 June. The ship's air group then consisted of 18 Nakajima B5N torpedo bombers and 16 A5M4 fighters. When the First Air Fleet was formed on 10 April 1941, "Ryūjō" became flagship of the Fourth Carrier Division.