From March 1937 he was the commander of the 8th Independent Training Battalion, and was promoted to colonel in November of the same year. In March 1939, he was appointed commander of the Utsunomiya Regimental District, a recruiting and training unit responsible for raising troops in Tochigi Prefecture. Okabe was assigned command of then IJA 13th Infantry Regiment in October 1940, and was promoted to major general in August 1941. He led the regiment at the Battle of Changsha from September 18 to October 6, 1941 including after his promotion to commander of the IJA 51st Infantry Group. In July 1942, his forces were transferred to the command of the Japanese 17th Army and reassigned to the Solomon Islands, and subsequently to the Japanese 18th Army, where they went into combat during the Salamaua–Lae campaign. He led the "Okabe Detachment" along the Black Cat Track and at the Battle of Wau. IN May 1943, he was rotated back to Japan and attached to the Eastern District Army, which was responsible for defense of Tokyo and its environs. In February 1944, he was appointed commander of the IJA 32nd Security Unit based in Hokkaido. In March 1945, he was made commander of the IJA 79th Independent Mixed Brigade, which was sent to Andong in souther Manchukuo, where he remained until the surrender of Japan.