Soemu Toyoda
With the start of the Second Sino-Japanese War, Kobayashi became Chief of Staff of the IJN 4th Fleet and was based at Tsingtao as an assistant to Rear Admiral Soemu Toyoda. On 1 December 1937, Kobayashi was promoted to rear admiral. From September 1938 to November 1939, he served as Chief of Staff of the Sasebo Naval District. He returned to the China front in November 1939 as Commander of the Naval Base Forces in Wuhan, and from November 1940 in Shanghai. He returned to Japan in May 1941. On 15 October 1941, Kobayashi was promoted to vice admiral.