Akamatsu was credited with shooting down 11 enemy aircraft over China in the Second Sino-Japanese War, including four in a single engagement near Nanchang on 25 February 1938. In the opening months of the Pacific War, he served in the Philippines and Dutch East Indies campaigns. From January 1944 until the end of the war, Akamatsu flew out of Atsugi Air Base, defending Tokyo from Allied air attacks.