 Complete the following phrase:  In December 1937, Kofukuda was promoted to full Lieutet and assigned to the carrier Ryūjō as its fighter squadron leader Buntaichō. In June 1938, he was posted to the 12th Air Group in Central China, which operated from Nanjing at that time, but then gradually moved to Anqing, Jiujiang and finally to Hankou with the 