As a lieutenant during World War I, he served on the cruiser Asama, followed by the battleship Kashima and destroyer Hamakaze, but was not on any combat missions.

After Kusaka's promotion to captain on 1 December 1930, he was sent overseas to the United States and Europe for one year.

On 28 September 1942, he took command of the 11th Air Fleet located at the major Japanese base of Rabaul on New Britain in the South Pacific.

As commander, Kusaka directed the employment of naval ships and combat personnel involved in the fighting against Allied forces advancing up the Solomon Islands chain and New Guinea and New Britain towards Rabaul.

[3] On 6 September 1945, Kusaka, acting as the senior officer for Japanese naval forces in the Rabaul area, along with General Hitoshi Imamura, the senior Imperial Japanese Army commander for the area, surrendered Rabaul to Allied forces.